There are lots of things! The smallest option would be a costume, but you could even get someone who wants to be a Cowboy a horse if they are old enough.
A Good Gift for a boy who wants to be a cowboy is a cowboy hat or boots
cowboy boots
horse
boots hat whip
Boots hat horse
boots hat whip
a cowboy hat boots gun horse rope guitar
a toy gun or a gutair
A good birthday for a kid who wants to be a frikin cowboy is jade so he can make out with his city girlfriend and they can have rubber kids...hahalol
A good gift for an imaginative little cowboy is a classic cowboy hat and boots. Or, a Woody (from the Disney movie, Toy Story) action figure. A toy horse and a banana is a nice touch.
cowboy hat, toy gun, rope, horse, cowboy boots, guitar
Cowboy hat, cowboy Boot's, gun,rope,guiter,horse.