The exception is the rule? I wonder what is the age distribution of programmers / engineers at google (I hear it leans heavily to the left). I suspect the perceived ageism at google and in IT in general is coincidental; It probably has to do more with human development maybe a natural tendency to for example:
* Not care as much about new tech, same old same old.
* Not really fit in with the younger culture in the office (this one is circular).
* Not willing to work over time without pay.
* Not wanting to live in over inflated regions.
* Not interested in studying for technical interviews (feel that it is not professional).
Maybe there is something inherent in big IT shops like Google that end up having the same end result that ageism would have; If the end result is the same, is it still ageism? I think so, but at the same time I think the problem is bigger than Google, that is a systemic problem in the entire IT field, one that might just be part of its very nature.
Please remember just because you are the exception, you might not be the rule. It would be much more productive to add that maybe there are a lot of 50 year olds at google etc. It is like someone seeing a war veteran and saying oh war x might not be so bad, that person made it out.