Is 37 too old to start playing tennis again and if not, can I play USTA tournaments?

I used to be really good and played up until I was 21. I started around age 5. I would love to play again but I'm out of shape! I get winded very easy. How should I get myself back into shape even before attempting to maybe take private lessons? I'm not overweight but just really weak! I also am a smoker so I'd have to give that up (obviously) but it's not easy. My main question though is that can I ever become really good again at my age???