One of the ladies I used to trail ride and drill team with had a colt who was a monster as a foal, she got him at three months and he would charge, kick, paw, bite, etc at horses and people alike. She gelded him at 5 months and he is now a sweetheart towards people, but will talk to and drop around any horses he is used to and will thump his belly a few times before putting his equipment away. He is such a weirdo, lol.
I've had a couple colts I bought as unhandled horses and kept from the time they were weanlings to over two years old, they never acted studdy with bad behavior and never looked at a mare, other than my first colt trying to nurse off one for a couple days when I brought him home off his mama, unsuccessfully, poor thing almost got his brains kicked out for trying!
Ladybug, is your colt already exhibiting symptoms of being a problem child?
I've also seen a lot of very young foals jump up on their dams, it may look like they were trying to mount, but my filly did it all the time in play.