Mature barred hens will have a red comb and red wattles, just smaller than the males. Some hens take a little longer and might not reach maturity until 20 to 22 weeks, some get there sooner.
At 18 weeks if this were a rooster I would expect to see at least the beginning of saddle and hackle feathers and many will be crowing by then.
They also would have a "roo-ish" stance and generally be much lighter in overall appearance...more silver grey looking than black with white bars.