Comb shape, isn't reliable either. Many of my U shaped combed chicks turned out female, combs stayed flat, or slightly bumpy. Posture, & behavior aren't great indicators all the time, you can get females that are more dominant, & have males that are more skittish/submissive.
Comb shape, & size varies, with both sexes, but usually there is a pretty consistent growth rate of combs of males. They tend to get more raised/larger as the chicks grow.
Personally I'd wait between 6-12 weeks, & see if there's any changes. It'll be more obvious once they hit 4-6 months old though.