i got interested in MMA when I was 21. during that time, i lived 10 minutes away from rey diogo's school but didn't know who he was, and was too lazy to make the trip to his school and take his classes. at 22 i moved, and signed up at a new gym and only took classes sporadically. i didn't start taking classes seriously until i was 24 and had started working.
i kick myself everyday for not having gone to rey's school when i had the chance, and not having gone to class consistently while i was in college and had more free time.
start right away. once you fall in love with the art, you will immediately feel regret at not having started sooner, like others here have expressed.