I'd say still a little too early to tell. Watch his/her comb development closely though, a boy's will get bigger much faster and be a darker red. That's a pretty good indication that you've got a roo on your hands.
How old is it? If you want an early guess go by feather development, it's not 100% correct, but it's a good guess. Roos get feathers slower, they have more to develop. Hens get them 2 times as quick. So far I'm pretty sure all 6 of my chicks are hens, they were sexed. And they are getting feathers pretty quickly. You'll only know what sex they are until they reach 6 weeks. Don't rely on feathers.