My son is 2.9 and bright. OK ... still quite young, but he's very energetic/hyper and I'm not sure if he would settle at school. (he's a May birthday and all the school round here take them in September so he'd only just be 4). He is quite immature despite being v bright and I've had to pull him out from pre-school as he has been charging round like a loony and has pushed kids. He also still needs a nap (sometimes 2 hours) which I can't see him dropping any time soon.
I've been considering home schooling for the first couple of years of school as it would give him time to mature but my Mum is really worried he won't fit it if he starts school late.