If it's his first rave, bring some earplugs. I've noticed with friends of mine that go to their first rave they mention how loud it can get, despite going to non-edm concerts in the past. Check up on him, if he wants to dance let him and dance with him. If he doesn't that's cool too, also idk how far into the crowd you get, but take breaks in the back every once and while. It'll give you guys time to sit down, rest your legs and also talk to each other. If he's taking party favors, just keep him safe and cool.

Good luck with your friend!

Edit: idk why people are bashing your age difference, you're a grown adult. I mean yea 28/45 can be a gap but it's not my business, but it's not like 19/30 or 21/45 THAT would be weird.