AFM acts like a musician's union. Yes, it would be an appropriate organization for someone like this young man. But I'm not sure you can join for someone else, or would want to. An offer to pay the dues, done up on a certificate or something, might be the closest you could get to it. My kid doesn't belong yet (although I expect he will one of these days) so I don't know too much about it.
I'm thinking that there might be other organizations more appropriate to "gift." My kid belongs to a "horn society." I don't know if something exists for guitars, or for bands.
There are magazines, such as [edit - this one for bass guitar]
Home
[Can also get it through Amazon, with a gift card, but CC TOS doesn't allow Amazon links, I don't think.]
There are a bunch of books out there, and any of them might be appropriate. I don't have personal knowledge of any of them - so if anybody else is familiar with them, please weigh in! Here are a couple:
*Legal Aspects of the Music Industry: An Insider's View
*This Business of Music Marketing and Promotion, Revised and Updated Edition
*This Business of Music: The Definitive Guide to the Music Industry
*Secrets of Negotiating a Record Contract: The Musician's Guide to Understanding and Avoiding Sneaky Lawyer Tricks
Unfortunately, I just don't know as much about the kind of music that plugs in. Bassdad is an electrical engineer - he might know some really cool gadgets that a recording engineer would drool over.
Missing the trombone... I'm not sure. I suspect that's individual. Since he will still be involved in music and performance, the trombone might not leave too big of a hole.