I have a gelding that was a stallion into his 20's (a rescue - exact age unknown) and he will still drop, fully extend and even penetrate mares in certain conditions. I personally don't want any penetration going on (even from a gelding) because it's just not healthy and clean and why risk an infection? So I keep Wiz away from certain mares at certain times of the year to prevent this. But he will still "protect" his herd of mares and run the fenceline with Spirit and try to show his stuff. He herds his mares away from Spirit - it's very funny actually to watch. It's really not that uncommon at all for a gelding to still exhibit stallion-like behaviors - to varying degrees.
Give him more time - it will probably get better is my guess.