My son is 3 in January so slightly younger but likes to play with his older brothers toys, in general he likes:
Avengers figures and dress up
Fireman Sam (mainly the engine)
Dinosaurs
Toy cars (we put our toy garage outside over the summer so they don't use that as much anymore)
Wooden train track
Football
Books
Duplo
He's also just starting to enjoy sitting down with arts and craft bits and actually making something. He'll also play some board game type things with his brother but I'm not sure if he'd try them on his own yet - we have loads of matching pairs game, bunny jump, hungry hippos and for Christmas he's getting pop up pirate