I think an absolutely great use for an old server at a youth center would be whatever the kids decide to use it for. Seriously, put it to a vote. There are lots of fun options, like a Minecraft server, one of the various Discord alternatives, a private wiki, or whatever else you find on the Awesome Selfhosted List . Just let it be their choice.

And, more importantly, set it up with them. Let anyone who wants to be involved in the process join in. If you're kind of a newbie to Linux yourself, that's even better; let them see you fuck up. Let them help you search for answers when you run into problems. Make it into a collaborative project.

Now, as for the actual hardware you have there... Man, that thing is ancient. If it's what you've got it's what you've got. As I've already indicated I think the process is worth more than the result here. That said, if you look around you can almost certainly find a refurbished old corporate PC for a hundred bucks or so that will be more powerful. Liquidation auctions are especially good for that kind of thing.