Although I wouldn't jump to assume that he isn't already an active person, I will share a bit of my own experience (as someone who recently turned 18):

Try to limit your time working with computers. Really. I used to waste a ton of time installing new Linux distributions, customizing my desktop, learning how to use vim, learning new programming languages, etc. Not that this was bad in any way, or not enjoyable. But did I really need to spend as much time as I did?

I had a conversation with a few of my friends that got me really reconsidering a lot of this. One of them asked me, "What do you like spending your time doing?" To be honest, my favorite thing to do is be with other people. Or at least, the most rewarding and vivid memories I have were with others. Programming can very frequently turn into a solo journey that consumes hours of my time. It's fun, but also isolating.

If you limit your time with your computer (say, a max of 1.5 hours per day unless you're doing homework -- this will vary from person to person, but you have to be honest with yourself), you'll do more of what you actually enjoy doing while you're on a computer, and you'll also find opportunities to do more of what you enjoy off of it as well.

I surf Facebook less, I spend less time needlessly checking my email, and I only use HN or Reddit as a break from doing projects. That's how I make things more interesting for myself, and I also wind up going out a lot more than I used to.