They are waaaay too young to try to sex, some people say they can sex from the first set of leaves, but I think it's bs. If you just want to harvest a little bit, and you're growing indoors, bump up the light cycle to 18/6 or 20/4 for the next couple weeks, this will help them get a bit stronger before you switch them over to a 12/12 (or 11/13) flowering cycle. They won't be very big, but you might get a few grams off them. Have patience, growing weed isn't something that can be rushed.