You can do whatever you want, you don't have to give up one thing for another. I have a huge gap difference between my hobbies same as your nephew. The only thing is if you dedicate yourself to many things at once you wont be as good at it than dedicating to it alone.

If you try and practice them both at the same time its the ultimate art, throwing punches while simultaneously slaying your guitar like Eddie Van Halen is a joy to behold!

I got a friend who stopped playin basketball just bc he broke his finger in a gamel before a major concert.... the poor guy played guitar that night w/ his left index finger broken, he did good and got paid bigtime but swore to give up basketball...

yes just it depends on your dedication

My nephew has been doing martial arts- kickboxing, actually- since a very young age, he's quite good too and he loves it. Now he's 15 and he recently started learning playing the guitar. He loves that too, but he's worried he'll have to give up fighting in order to improve. Anyone has a similar experience? Can you do both things at the same time?