As an aspiring game developer, I look at Valve's actions with a lot of excitement lately. Steam and Source are coming to Mac for sure now, and so that means Source SDK should be updated to support deployment to Macs. If Linux is included in this package, it only sweetens the deal. For developers just getting started, Source would have a unique advantage over the other engines available currently (e.g. Unreal, Crytek) in that it would allow developers to reach as wide an audience as possible. I really hope this happens.

I agree that there is most likely some other factor involved. Correlation does not equal causation in this case. That is to say, yes, people tend to reach their intellectual peak at 22, and start waning by 27. However, the reason for why it does this has not been touched upon at all at this point.

It could for example, have nothing to do with natural aging, but have everything to do with the fact that most people are out of college by then and working. If you're not exercising your mental muscles by constantly learning new things, of course you're going to get dumber.