I can not tell you how many times I encounter people who say, "I'm happy with the way I am right now, but I am sure I'll need to start working out eventually." While I am all for enjoying life while you can, I will say that it is A LOT easier to integrate an exercise regime into your life when you're happy with how you look and feel, rather than when you're doing it because you need to lose the weight (health and/or aesthetic reasons).
Exercising can only better your life, no matter when you start it. Since most people wait for a reason to exercise such as: Suddenly realizing they're overweight, having the doc tell them they have to for health reasons, wanting to lose 15 pounds to fit into that bikini. I won't even go into the bad reasons I've heard. Ask anyone who's had to hit the gym because their doctor told them it was that or Type II Diabetes -- Not so fun. This pressure makes getting active stressful rather than enjoyable. However, if you start now and make it part of your life, you may actually start to enjoy it. Gasp, I know, but it's been known to happen. Start small by adding a weekly walk (or jog), yoga class or even a trip to the gym, you won't regret it.
So even if you're happy with the way you look and feel, why not hit the gym? It can only make you feel even happier and better.