I'm quoting MacTracker. It may not be up to date with the latest ram stick sizes.
Checked up on the Apple Support page, it's all over the place, Dual 1.8 listed twice, once with 4gb and one with 8gb. Even if it only has 4gigs, I could see it still being a beast.
Idk, I just guess for the 14 year old, G5 for sure. More than enough Muscle to play any PPC games he might come across ( I'm finding more and more ), its big, looks cool, and mines been rock solid.