Many times you can't
Some you can in a couple of weeks if they are color sexes
When some rows of feathers come in
Some you can't tell at all until their actually crowing or laying an egg
Some you can by sex link
And some
You thought was sure a hen, even at 3 months and it was a rooster
I Gage a lot by having the same breed hatch, then compare as they grow by size of comb..Attitude, strut, etc
But iam new to this
Iam stoked some of my next two hatches are wheatens so I should be able to tell in a couple of weeks
And yes, some you can tell by how they feather out and that's the wait also..etc
Vent sexing also
So hope the pros chime in for u