All I do on the weekends in the states was drink and livestream. All I drink is Crown Royal, with a whatever soda I have in my room which is mostly Cream Soda. However, when I'm not drinking that I only like fruity drinks which you said he won't like. However, I'd recommend if he doesn't like the taste of alcohol to get wine coolers, like Smirnoff Ice which is really good. Almost every flavor. If he'd like to try something fruity a Drunken Buddha is really good. However, if it's his 21 birthday, I saw go all out and have him try EVERYTHING! I didn't get to celebrate my 21st birthday sadly, so I want to have everyone be able to experience it at it's best. Have him try everything, if he doesn't like anything, after trying them all at least he'll start getting a little tipsy, and then realize everything tastes better.
I know, I got trashed and had the best tasting alcohol ever, it was Maple Moonshine, and I was drinking that shit like it was soda. I tried it the next weekend when I was at another party, it wasn't drunk and it was the worst tasting drink ever lol.