If you reduce everything that Lyons is saying that that one quote from the CEO, perhaps the evidence is slim. But if you take the observations he's making together, as a whole, a different picture emerges
I guess I don't see the fact that there's beer in the fridge or that people drink at work as evidence of the CEO's ageism. It seems to be evidence of a relaxed attitude towards alcohol.
Similarly, calling thirty-somethings "old" is...maybe insensitive? I dunno, maybe it's ageist. I'd think it would be hard to say without being there.
Clearly the author feels discriminated against, because his CEO doesn't see how amazing he is at his job. It's definitely his right to feel that way, and who knows, maybe he's right, but in any case I'm not inclined to take his observations as direct evidence of discrimination.