Everyone's right so far... need your PPL first, although you could take an aerobatic lesson any ol' time.
As far as a career goes (airshow or competition performer), one thing that all of those folks have in common is a tremendous amount of hours logged doing aerobatics. It's a lot of fun (I have 1 hr. of dual in a Zlin 242 logged), but it's hard work, and after getting your body used to it, you need to do it regularly, like an athlete staying in training. But there are all sorts of levels of shows and competitions; you could probably start showing off almost right away, once you get the hang of the basics. Finding sponsors who want to pay you to go nuts in an Extra, Sukhoi, or whatever- there's probably a different story for every sponsored pilot out there.You're not going to see a job like that in the classified ads.
And don't even think of trying to finance a high-level aerobatic plane on your own, unless you're filthy rich. They all have sponsors, even the ones who have "regular" jobs on the side (airline pilot, etc.).
If you just want to do it for fun, ignore all I've just said and find an instructor with an aerobatic plane for rent- he or she will answer any other questions you might have. Go for it!!!
