Yeah I felt the same at 27. But then... you don't hit 30, 30 hits you. I'm not kidding.
Then "once you hit the real world and have to get a real job that college metabolism of yours will shut down and you'll pack on the pounds like everybody else."
Then "just wait 'til you're 25 like me and your hair starts falling out".
Then "When 30 hits and you don't have any energy anymore then you'll understand"
... And so forth. But thus far none of it has ever happened. I think that people let themselves fall apart, then notice the date and assume that must be the reason. But if you don't wan't to have that happen, you can make a point of staying in good shape for a long time.
That said, I'm sure there's some new inevitable milestone waiting for me when I hit 44. It's definitely going to suck.