Since I've been watching a bit of the Winter Olympics...
You hone your athletic skill as a teenager and hit level 10 before your YA birthday. Congratulations! Now you don't have to worry about training to be an athlete, soldier, cop, or criminal. Like, ever. You have absolutely nothing else to learn athletically, no matter how you choose to apply your talent. You'll never need to work out again, and you'll still be in perfect physical condition for the rest of your life. You can literally go your entire adulthood without so much as changing into your workout clothes, and your pace on the treadmill will be the same on the day you die as it was when you were in high school. In fact, you can even win the Amateur Olympics as an elder—just make sure to get a good night's sleep and eat an entire plate of Baked Angel Food cake before you go.