I would agree that it's too early to tell. You will probably have a few indications that will help you lean one way or the other around 6 weeks old. Just keep an eye on the comb. Do you have any other chicks the same age that you can compare as you go? You are looking for size and color, if it starts to get pink around the 6 week mark (maybe sooner, depends) where the others are still yellow, then you might have a roo. By 8 weeks you should be fairly certain but I completely understand wanting or needing to know as soon as possible. Also, if you have others the same age, compare the feathering rate, if some are feathering faster than this one, then this one could be a roo, they tend to feather slower than pullets. You will hear around here "you won't know for sure until you get an egg". Honestly, that's pretty true. Even pullets can crow so that's not even a positive.
I know it's hard to wait, I'm sorry that there isn't a better way to tell.