Clevian:
Start NOW! Start with ballet classes -- they form the stucture and technique for all other dance forms. I know a lot of jazz teachers who insist that their students also take ballet.
As for age, there's no real magic age that a male dancer has to start by to have a professional career. As Joe said, some professional ballet dancers started earlier than 16, but I know of several that started in thier high-school years.
Don't worry about what people may think about a boy in tights! I'm not saying that people won't think stupid things, but want you to know that the reason for wearing tights is purely functional, to allow you to move freely, and they're important for your teachers (and you) to see how the muscles in the body are working.
I could tell you that nobody mocks a welder because he wears funny gloves and an apron, so people shouldn't mock ballet dancers in tights. The fact of the matter is that many stupid people do say bad things about ballet dancers in tights. But know that there are good reasons for you to wear tights when your dance.
What's more important is that you should follow your heart! If you love ballet and dancing, go for it. It doesn't matter what other people will think if you're happy with yourself![/i]