Soxprospects.com: Top under-20 prospects

Albert Pujols. Alex Rodriguez. Joe Mauer. Hanley Ramirez. Felix Hernandez. Zack Greinke.

That is a list not only of some of the game’s biggest stars, but of players that all began their professional baseball careers as teenagers. Age may be just a number, but it can tell you a lot in the area of baseball development. Players that succeed against age-advanced competition in the minors often end up having the most success in the majors, while older minor leaguers who excel against younger opponents tend not to replicate that success when appropriately challenged. On that note, let’s take a look at the top ten prospects under the age of 20 in the Red Sox system:

1. Reymond Fuentes, CF

Age: 19 years, 3 months

Signing Bonus: $1.134 million (July 2009)

2010 Assignment: Low-A Greenville

Numbers: .277/.336/.412, 2 HR, 13 SB in 13 attempts

The Report: Boston’s 2009 first-round pick, Fuentes is an athletic center fielder with elite speed, a quick and compact stroke, and a strong offensive approach. He shows good reactions on balls on the inner third of the plate and projects as a hitter with gap power as he matures physically. Fuentes has the defensive skills to stick in center field, showing plus defensive tools with the exception of his below-average arm strength. The Puerto Rican outfielder has drawn comparisons to Jacoby Ellsbury and Carlos Beltran, who happens to be Fuentes’ cousin. He has looked good early on, although 29 strikeouts in 111 at-bats is somewhat of a concern. Then again, he is 18 months younger than the average player in the South Atlantic League, and he is still in the midst of adjusting to facing professional pitchers on a daily basis.

“Reymond is doing well -- getting acclimated to his first full season,” said Red Sox Director of Player Development Mike Hazen. “He’s been very good on defense and on the bases, and we hope he will continue to do so. He’s still continuing to learn on the offensive side -- especially what his pitch is and which ones are not.”

2. David Renfroe, 3B

Age: 19 years, 6 months

Signing Bonus: $1.134 million (August 2009)

2010 Assignment: Extended Spring Training

Numbers: Yet to debut

The Report: Heading into the 2009 draft, Renfroe was actually more highly-regarded than Fuentes by many scouts. However, he slipped to the third round, likely due to high bonus demands, and ultimately received first-round money in the form of an identical bonus to that of Fuentes. A multi-sport athlete and a two-way player in high school, Renfroe brings solid all-around tools and an excellent baseball acumen to the table. He has a smooth swing that produces excellent backspin on the ball, and he has demonstrated above-average power potential that should begin to show as he improves his pitch recognition. A shortstop in high school, Renfroe moved to third base during the Fall Instructional League and will likely start his professional career with Lowell this June. For now, he remains in Fort Myers at extended spring training, working on adjustments to his offensive approach.

“They just want me to be a complete player mentally and physically while taking in everything I can while I’m at spring training,” said Renfroe during spring training. “Coming here and having a specific routine every day is something the organization really stresses. I just want to make sure I have a routine that works for me in order to someday reach the majors.”

3. Madison Younginer, RHP

Age: 19 years, 6 months

Signing Bonus: $975,000 (August 2009)

2010 Assignment: Extended Spring Training

Numbers: Yet to debut

The Report: A right-hander given supplemental first-round money in 2009, Younginer has electric stuff and an arsenal that could round into a potentially devastating three-pitch mix: a mid-to-high-90s four-seam fastball, a 12-to-6 curveball, and a low-80s changeup. In 2010 the right-hander will need to work on cleaning up his delivery to develop a consistent release point to enhance his fastball command and continue to work on the feel for his changeup, which showed good progression during the 2009 season leading up to the draft. He will likely follow Renfroe to Lowell, where he should show flashes of dominance. A true test for Younginer will be how he is able to maintain focus playing against advanced batters in front of his hometown crowd once he advances to Low-A Greenville.

In the long run, Younginer has amazing potential, and the flamethrower’s success will hinge on refining his arsenal through advances in the finer aspects of his mound approach. “Madison has had a very good camp,” said Hazen, “we’re still working with the overall command of his stuff and repeatability of his delivery.”

4. Roman Mendez, RHP

Age: 19 years, 10 months

Signing Bonus: $125,000 (July 2007)

2010 Assignment: Greenville

Numbers: 0-2, 11.40 ERA, 19 strikeouts, 11 walks, 15 IP

The Report: The Dominican right-hander signed with Boston at the age of 16 on the first day of the early international free agent signing period in July 2007. He has shown a lot of promise, particularly due to the strength of his fastball, which has topped out at 96 mph at an early age. Mendez also makes use of a 79-81 mph slider with plus potential and a mid-80s changeup, both of which are works in progress. The hurler breezed through the Dominican Summer League in 2008 and the Rookie-Level Gulf Coast League in 2009, putting up a combined 2.32 ERA and striking out 93 batters in 100.2 innings over that two-season span. That success earned him an aggressive promotion to Greenville in 2010. He has struggled to find consistent control with the Low-A Drive out of the gate, and has been knocked around a little bit in six early starts. He was placed on the disabled list with a left knee contusion on May 8.

5. Michael Almanzar, 3B

Age: 19 years, 5 months

Signing Bonus: $1.5 million (July 2007)

2010 Assignment: Greenville

Numbers: .17/.279/.350, 2 HRs

The Report: The son of former major league pitcher Carlos Almanzar, the Sox gave 16-year-old international free agent Michael Almanzar the equivalent of mid-first-round money in 2007, well more than any Boston draftee received in bonus money that summer. Now 19, the third baseman has flashed a lot of potential in every aspect of the game -- especially in the power department -- but his development has been slow thus far. While he regularly puts on a show in batting practice, he has struggled against off-speed stuff and his lower-body swing mechanics continue to be a work in progress, leading to subpar offensive numbers. His defense is also still suspect, having already committed 9 errors this season after committing 20 in 92 games in 2009. However, Almanzar has shown some improvements in the areas of game power, pitch recognition, and plate discipline early in 2010, his third go-round with Greenville.

“Michael has made some good adjustments in spring training, standing more upright and attacking the baseball,” said Hazen. “He has done pretty well early in the year with consistency, but we’re still working toward the day-in-and-day-out repeating of his set up and swing.”

6. Jose Vinicio, SS

Age: 16 years, 10 months

Signing Bonus: $1.95 million (July 2009)

2010 Assignment: Extended Spring Training

Numbers: Yet to debut

The Report: Boston signed the switch-hitting Dominican shortstop on his 16th birthday in 2009, handing him one of the largest signing bonuses given to any international player by any team last year. Right now, Vinicio’s frame looks more like that of a little leaguer than a major leaguer, but he has already shown flashes in spring training of why Boston gave him such a large bonus, demonstrating outstanding defensive tools, a quick bat, and an impressive level of confidence at the plate. A major determinative factor for his major league potential will be how well he grows into his frame, but with some projection, he looks to be a Jose Iglesias-type player at this point. Look for the shortstop to begin the 2010 season in the Gulf Coast League, where he could be the youngest player in the entire league.

7. Brandon Jacobs, OF

Age: 19 years, 5 months

Signing Bonus: $750,000 (August 2009)

2010 Assignment: Extended Spring Training

Numbers: .250/.333/.333 (2009 stats in 24 at-bats with the GCL Red Sox)

The Report: Prior to being drafted by the Red Sox in the 10th round of the 2009 draft, Jacobs had committed to play running back at Auburn. It took early second-round money to buy him out of that commitment in August 2009, at which time he immediately began his professional career in the Gulf Coast League. At 19, he already has a major league body, and he probably has the most power potential in the entire Red Sox system right now. Jacobs shows natural loft and lift in his swing that should translate to higher home run totals as he continues to sharpen his approach and pitch selectiveness at the plate, which appeared to be areas of focus for him during spring training. He also has above-average speed, but his defense remains a liability at this early stage of his career, leading most scouts to project him as a future left fielder. His overall game is very raw, but with his mix of power and athleticism, he has the potential to be a middle-of-the-order bat at the major league level. He will likely start his season with Lowell when the Spinners’ season gets underway on June 18.

8. Seth Schwindenhammer, OF

Age: 18 years, 10 months

Signing Bonus: $140,000 (June 2009)

2010 Assignment: Extended Spring Training

Numbers: .194/.252/.274 (2009 stats in 124 at-bats with the GCL Red Sox)

The Report: Drafted in the fifth round in 2009 out of Limestone Community High School in Illinois, Schwindenhammer signed immediately and began his career in the Gulf Coast League prior to his 18th birthday. A left-handed bat with big-time power potential, the outfielder struggled in his first stint against professional competition, which can often be the case for young draftees coming from northern high schools. Look for an improved performance in a return to the GCL this June.

9. Oscar Perez, C

Age: 18 years, 6 months

Signing Bonus: $750,000 (July 2008)

2010 Assignment: Extended Spring Training

Numbers: .210/.289/.292 (2009 stats in 195 at-bats with the Dominican Summer League Red Sox)

The Report: A catcher with advanced defensive tools out of Venezuela, the Red Sox made Perez their top international bonus baby in 2008 after Junichi Tazawa. Boston’s scouts were quite high on the backstop when he signed, deeming him to be in the upper-echelon of the amateur catchers who signed in 2008, but other scouts have tabbed him as a back-up catcher at the big league level at best. Perez already has a major league body built for the rigors of catching, similar to that of Pudge Rodriguez. However, his offensive game is unrefined, and he was unable to find much success with the bat for Boston’s DSL club in 2009. He is expected to play in the GCL in 2010.

10. Miles Head, 3B

Age: 19 years, 0 months

Signing Bonus: $335,000 (August 2009)

2010 Assignment: Extended Spring Training

Numbers: .103/.188/.103 (2009 stats in 29 at-bats with the GCL Red Sox)

The Report: Head was selected in the 26th round of the 2009 draft and given the equivalent of a late-third-round bonus. A third baseman with plus power potential, Head has sound swing mechanics but his plate discipline needs work. Defensively, he has an excellent arm, decent range, and an average-to-below-average glove. He likely will be assigned to play in the Gulf Coast League with Vinicio, Schwindenhammer, and Perez in June.

Mike Andrews is designer and developer of SoxProspects.com and a special contributor to ESPNBoston.com.