My son is 4 years old and is obsessed with his sister's Glimmer Wings Rainbow Dash. I also bought him a plush Rainbow Dash and a plush Applejack because he wanted them. I never yell at him for playing with his sister's toys, she will, but I won't. He is autistic though, so anything that he shows interest in and and relate to then I'm all for.
I would suggest Rainbow Dash as Shadowbolt since it has a boyish superhero look to it.