I have an October birthday so I had the option too - I started school "early" but was glad I did, as I was the kind of kid that was easily bored in school.

I think you have to do what's right for your kid - especially in line with where he is re: learning. I know that a lot of people hold their kids back (or don't start early) so that they'll be bigger, older, stronger, etc. for sports (especially boys). I'm not a fan of this practice, because for me school is about education first.

I say, if your son seems "ready" then go for it!