Sorry, it will be a while. They will all look like females until sexual maturity, when the males anal fins will begin to develop into gonopodiums.
The biggest, boldest males will develop first, the others after.
If they are feeling crowded, or there are more males then females, or some older, dominant males, you will even see a few "mock" females. These are boys who just won't develop until the pressure is off. It's more common in swordtails, but does happen in the related platies (not all platy species will do this, but many are hybridized, and also hybridized with swordtails).
I actually had one very recently. There was a tank with some nice big swordtails at the LFS, only 2 this color I wanted. I brought home my 2 "girls" and 2 weeks later, one developed a gonopodium and is developing a "sword". He is as big as males get, he just never matured until there was no competition.