I agree with Xero, take him to a class or two and see if he likes it. I really dont think it would change "sexual preference". There are plenty of perfectly straight men in ballet. Any activity is good for a child, and if hes interested in ballet, let him try it out!
PS. lots of ballet moves are strictly oriented at men when they do ballet, so dont be worried bout tutu's or too many pliets
I know this cuz i danced for 8 yrs, jazz, but i watched many a ballet class with boys in it
