Modern dance is filled with great male dancers who didn't start classes till they were in their late teens, or even early twenties. People can get good at tap at almost any time of life. You should try all three if you're interested.
You should start by taking ballet, at least three classes a week. And no matter what kind of dance you eventually focus on, you should make ballet class a life-long practice. The awesome thing about dancers today is that many of them are good at everything. I saw American Ballet Theatre do a Martha Graham (modern) piece beautifully this past spring. And Julio Bocca (GREAT male ballet dancer with American Ballet Theatre) did three months on Broadway this year doing "Fosse", which is jazz dancing.
Follow your dream. Get into class. Like the jocks say: "Just do it!"
Joe[/i]