J.C.
This is totally up to you. I think basing your decision on what is socially acceptable is the wrong way to decide. If you don't mind that people may mistake him for a girl, then it doesn't really matter what his hair looks like. It's just whatever you want. I chose to keep my son's hair short because I love the little boy look. I know of a couple of boys who have had longer hair though, my nephew for one. His mom cut it when he was two because she got tired of having to always say "no, he's a boy"