How can I tell him to change outfits?

Yo/ guys. i am 15 years old. I am in realtionship with who younger than me. He is 13 years old. HE is cute, he love to me. but he is soso childish. I know he is only 13 years so he may be childish. I want to see him with printerest guys outfits.. His outfits are a little annoying for me. like batman t-shirt... ext. how can i tell him? to change outfits. I am little scared to tell him. because he may be worry.
How can I tell him to change outfits?
Post Opinion