I was having this discussion with a friend the other day, and was wondering what others thought? I personally think its before you're comfortable with your sexuality/gender identity :3
When's too early to come out? Before you're ready. Before you've come to terms with and accepted those aspects of who you are.
I think it's best to do it as soon as possible. But of course you need to be ready and analyze your situation. I just don't think it's smart to wait too long. Especially in 2014. I mean why waste time?
I was just thinking, cos what if someone rushes into into it and it turns out they're not who they thought they were?
I actually think it's never too early, as long as you make the choice yourself. If you're outed that's a different story. But I don't think you have to be sure or comfortable with the idea necessarily, coming out can help those things along--especially if you've got someone to talk to and some perspective on the whole matter.
I think if you're exceptionally young, then maybe... But I guess my biggest problem with coming out is when people do it because of a date, or a possible relationship. You should come out for YOU.
When you can't do so safely. For example LGBT children of overly homophobic parents should consider waiting until they can support themselves on their own. There's foster homes for abandoned gay youth for a reason.
As long as you're comfortable with you being you and who you are, then I don't think it's ever too early to come out. But make sure that you are comfortable, and that you are completely, entirely sure.