My DC doesn't like anything on his head - rips off his hat. And at the weekend when we tried to wrap him in toilet paper (to be a mummy) or have his face painted at a Halloween party, he resisted. He tries to rip the stuff off.
He's not at all interested in it - is he too young? His friend, same age, but a girl, really liked it...interestingly...
My DS1 is 4 and still doesn't like dressing up, never really has (I think up until about 2.5 I got away with dressing him in costumes, but since he learned to undress himself it's been a non-starter). He is unusual among his friends, but there is one other little boy in nursery who doesn't like dressing up either.
For Halloween he as going as a wizard in disguise as a normal boy . He has however learned a very good magic spell to try out on people when trick-or-treating, it's not the role play which he objects too, just the costume.
DS is 22mo and likes dressing up in hats sometimes - only ever on his terms though, he won't put one on unless he wants to (and he has a special "hat face" to accompany them). I'm fairly certain he wouldn't let face paints anywhere near him or be wrapped in toilet paper as he hates to be interfered with or to have anything in his way. I imagine a costume will be ok as long as he doesn't know it's a costume - he quite likes clothes, especially if stripey!
DS aged 26 months would attempt murder before being subjected to being dressed more than necessary to get up and on with the day. All through this summer he has refused a hat, it would stay on for 10 seconds max and be flung. Now its a bit colder he will tolerate one when really really chilly. Some kids like some stuff, some prefer other stuff. I wouldn't worry about it.