Good question I have the exact problem with my 14 week old BR "hen", she likes to crow so she may be a he. I'm just going to wait and see as she/he gets older.
S/he is around 14-15wks... I was 100% she was a hen from baby.... Posted it on here and 98% said hen also... I am questioning it now... Not sure why either... It's actions around other chickens makes me say hen too... I haven't heard a single crowing or clucking noise from it except about 5 minutes ago and it was just a little cluck.
It better not be mixed! It came from ideal hatchery as a barred rock!! (I really don't care if it is mixed or not)
The reasons it's pattern is messed up is bc all these dark feathers are coming out and whiter crazy feathers are sticking out everywhere in there place! It used to be pretty perfectly striped... (There's no gold tint in "real" life I do see it in the pic though)
How old will he be before he starts mounting up on hens?!?