I can't comment on Facebook but at Google I see plenty of people in their mid 30s and beyond. I joined in my early 40s. Yeah, we hire a lot of new grads / younger folks (I interview a lot of new grads) but I haven't noticed any overt ageism in the groups I've been in. Plus, the people making the hire decision don't see the candidate anyways. You should/would most likely get called out by the hiring groups if you added in color/vague "cultural fit" references.

This is just my experience, though.