Spieth showed this potential in high school

There weren't many signs on Sunday that Dallas' Jordan Spieth is still a teenager. Heck, there haven't been too many signs of that since he burst onto the PGA Tour as a 16-year-old amateur at the HP Byron Nelson Championship, his hometown tournament, a few years back.

Even then, I remember marveling at how you had to really pay attention to realize that the kid was, well, a kid. He didn't talk like someone who was merely happy to be playing with golfers that he idolized growing up. He said he wanted to win, and it didn't really come off as brash. Why? Because he had the game to back it up. And he wasn't saying it as if it was some pie-in-the-sky proclamation. He really believed it.

He made me a believer in that 2010 Nelson. There he was, within range of the leaders as he started the back nine, only to falter and end up tied for 16th. But it was the way he handled himself amid what should have been huge pressure that has me sitting here, more than three years later, surprised but not stunned that he's a PGA Tour champion.

The 19-year-old won the John Deere Classic on Sunday with some tremendous shots and a little luck, too. But it wasn't as if this came out of nowhere; he's been in contention several times this season. On Sunday, he holed a bunker shot that looked destined for the water on No. 18 just to make the playoff, and he admitted that the shot didn't have any spin. He just got lucky. He then watched as David Hearn missed about a 4-footer to win on the fourth playoff hole. Finally, Spieth struck. He hit a great approach shot as Hearn and Zach Johnson faltered. A tap-in par secured his victory. It's a big one for a bunch of reasons. He now has full status on the PGA Tour. He earned himself a spot in the British Open. And he's in the top 12 of the FedEx Cup rankings.

It was historic, too. He's the first teenager to win on the PGA Tour in 82 years. Yep. It's been that long. Ralph Guldahl in 1931 was the last one. Herbert Hoover was in the White House. The United States has gone through 13 presidents since then.

Spieth does look different three years after his debut. He's stronger physically. Maybe mentally, too, though I saw a tough-minded teenager as I walked just about every hole of his four rounds with him back in 2010. The loose golf shirt and not-quite-perfectly-fit pants have been replaced with an Under Armour logo and a fashion that makes him look like he belongs. Of course, his game is proof of that.

Spieth did something few expected when the season began, opting to play in a few early sponsors exemptions on the PGA Tour (after deciding to leave the University of Texas after his freshman year to turn pro). In doing so, he was electing to use some of his limited exemptions, instead of going to Q-school or teeing it up on the Web.com Tour to try to qualify for the PGA Tour either of those ways. It was risky in that if he didn't play well enough quickly enough, he was giving away chances to earn money and work his way up the Web.com money list.

But Spieth did play well. Instead of the minimum seven exemptions, Spieth was able to secure more because of how well he played. Even before that putt on the fifth playoff hole on Sunday, Spieth was on his way to earning enough to be in the top 125 on the money list on the PGA Tour and get his card for next season. Now, of course, he doesn't have to worry about any of that.

Does this win mean Spieth is the game's next great young player? Too soon to tell, but don't be fooled by his age. Back in 2010, I saw a young man who was not in awe of his surroundings despite thousands of classmates, friends and family watching him -- and before he had to get back to school to finish some tests. He was only a junior at Jesuit College Prep then, but he played and acted like he knew he belonged out there. He never had any doubts.

He didn't look like he had any on Sunday at the John Deere Classic, either. Spieth learned some lessons from being in contention at various points this season. He learned from his lone year of NCAA golf. He attacked the hole and birdied five of his final six holes, getting into the playoffs when Johnson bogeyed the 18th. Spieth knew he had a huge opportunity, and he took advantage of it, much like he did in Dallas three years ago.

It's a mature young man who boards that flight overseas to play in a tournament that he didn't even have time to pack for. It's a major. Just don't expect Spieth to be intimidated by any of it. He's not flying over there to simply see what the British Open is all about. He's going over there to win. I suspect major victories are in his future -- the near future.