Well, I would have thought that to have a gamer PC, you'd have to either have well off parents or be well off yourself. This, combined with perhaps slower more strategic games (compared to consoles), would skew it significantly towards older gamers. Not hugely though.
Reminds me of the intermittant times when it is announced that 50% of gamers are female...hmm. Then you hear they might be talking about online solitaire or whatever. Still, you can prove anything if you ask the right questions, and I'd imagine that certain people would want to show that gamers are older than you'd think, to dispell the idea that games are just for kids.