If they are as old as you say they are, they would typically have some good saddle feathers by now to tell! Between 12 and 20 weeks, the saddle feathers usually come in good!
These chickens are 12 weeks old in my picture. You can see the one rooster I have in this group. The other two white(ish) ones have much lower and pale comes in comparison!
Some pullets can fool you with bigger and red combs. But at this size, nice good comb and red is a good sign before...