Top 10 UFC fighters under 25

"The Ultimate Fighter" reality series was good to Kelvin Gastelum. And vice versa.

Last year, Gastelum (9-0) was a cast member on TUF 17. He was the last pick of coach Chael Sonnen, but advanced to the finals on three consecutive finishes. One of the season's most memorable moments featured a wide-eyed Gastelum speaking on the phone to UFC female bantamweight champion Ronda Rousey, of whom he is a fan. The season culminated in an upset win for Gastelum over Uriah Hall at the TUF Finale.

And to think, all of that nearly didn't happen because of one thing: Gastelum's birthday.

Tryouts for TUF 17 were held on Sept. 17, 2012. That date was exactly one month and seven days prior to Gastelum's 21st birthday. TUF contestants must be 21 years old, due to the presence of alcohol in the house.

Gastelum, who was working as a bail bondsman at the time, had a 6-0 professional record and wanted to try out, but wasn't old enough. Before he flew to the Las Vegas tryout, he crossed his fingers, called the producers of the show and asked when the official cutoff birth date was for potential contestants. The answer came back Oct. 24, 1991 -- his birthday.

"I had seen the ad and had wanted to try out since I was 18," said Gastelum, who fought his first amateur fight during his senior year of high school. "I called them up and said, 'Hey, my birthday is on Oct. 24. What is the cutoff date for your guys' show?' They said, 'It just so happens to be on your birthday.'"

Now 23, Gastelum represents one of the most promising young fighters on the UFC's (or any promotion's) roster. He's set to face his biggest test this weekend, meeting Jake Ellenberger (29-8) in the co-main event of UFC 180 in Mexico City.

He still officially hails from his original gym in Yuma, Arizona, but Gastelum spent the majority of his training camp for this fight at the high-profile Alliance MMA academy in San Diego. He and former TUF 17 teammate (and No. 1 Sonnen pick) Luke Barnatt (8-1) lived on a sponsor's docked houseboat, complete with kitchen, satellite television and separate bathrooms, during their time in Southern California.

The Mexican American's placement on the card has taken on new meaning in recent weeks, as heavyweight champion Cain Velasquez and fan favorite Diego Sanchez were each forced off the event due to injury. That potentially places more promotional lifting on Gastelum's shoulders for the UFC's first-ever trip to Mexico.

Those developments have not altered Gastelum's mindset heading into the bout, though. Coming off a strong camp with a high-level team, Gastelum says he's ready to make the next step in his career, which would mean knocking off an opponent with more than five times as many professional fights as he has.

It's a situation he doesn't find at all intimidating. Despite being on the short side of 25 years old, Gastelum says he has actually been waiting a long time for this kind of opportunity.

"I was ecstatic when I got this fight," Gastelum said. "These are the fights I want. I want to test my skills and hopefully prove I'm the best in the world. I'm not nervous at all."

Including Gastelum, here are the top 10 fighters under the age of 25 currently in the UFC:

1. Michael McDonald, 23, bantamweight

Record: 16-3, 5-2 UFC

DOB: Jan. 15, 1991

Notable fights: Won by KO over Miguel Torres, April 2012; lost by submission to Renan Barao, February 2013.

2. Kelvin Gastelum, 23, welterweight

Record: 9-0, 4-0 UFC

DOB: Oct. 24, 1991

Notable fights: Won by split decision vs. Uriah Hall, April 2013; won by split decision vs. Rick Story, March 2014.

3. John Lineker, 24, flyweight

Record: 24-7, 5-2 UFC

DOB: June 12, 1990

Notable fights: Won by unanimous decision vs. Yashuhiro Urushitani, November 2012; lost by unanimous decision vs. Ali Bagautinov, February 2014.

4. Kyoji Horiguchi, 24, flyweight

Record: 14-1, 3-0 UFC

DOB: Oct. 12, 1990

Notable fights: Lost by majority decision vs. Masakatsu Ueda, January 2012; won by unanimous decision vs. Darrell Montague, May 2014.

5. Ray Borg, 21, flyweight

Record: 7-1, 1-1 UFC

DOB: Aug. 4, 1993

Notable fights: Won by submission vs. Nick Urso, April 2014; lost by split decision vs. Dustin Ortiz, April 2014.

6. Max Holloway, 22, featherweight

Record: 11-3, 7-3 UFC

DOB: Dec. 4, 1991

Notable fights: Lost by submission vs. Dustin Poirier, February 2012; lost by unanimous decision vs. Conor McGregor, August 2013.

7. Mirsad Bektic, 23, featherweight

Record: 8-0, 1-0 UFC

DOB: Feb. 16, 1991

Notable fights: Won by TKO vs. Joe Pearson, December 2013; won by majority decision vs. Chas Skelly, April 2014.

8. Justin Scoggins, 22, flyweight

Record: 9-2, 2-2 UFC

DOB: May 2, 1992

Notable fights: Lost by split decision vs. Dustin Ortiz, July 2014; lost by submission vs. John Moraga, September 2014.

9. Erik Perez, 24, bantamweight

Record: 14-6, 4-2 UFC

DOB: Nov. 19, 1989

Notable fights: Lost by split decision vs. Takeya Mizugaki, August 2013; lost by submission vs. Bryan Caraway, June 2014.

10. Thomas de Almeida, 23, bantamweight

Record: 17-0, 1-0 UFC

DOB: July 31, 1991

Notable fights: Won by unanimous decision vs. Tim Gorman, November 2014.