Disclaimer: I work at Google (opinions are my own)
How would the people filing the lawsuit know whether Google didn't hire them due to their age or for other reasons? I see posts all the time about people complaining they didn't get into company X because of some silly reason but frankly, unless you are the interviewer you likely will never know the reason. Shouldn't we wait to see the outcome of the case?
Indeed Google itself is not as diverse as we would like to be, but that's actually the reason we have these outreach programs: to try to get a more diverse applicant pool, which hopefully will translate to a more diverse workforce.
The average age being 29 doesn't surprise me because there are many more young applicants than there are older ones, since CS is getting more and more popular. Not only that but typically a larger company will have more junior developers than senior ones, and most junior developers are also more junior in age.
I don't know whether Google discriminates by age since I don't have the numbers, but I will say that Google takes diversity and inclusivity extremely seriously. I don't think a day goes by that I don't see a post asking for volunteers for some activity to promote diversity. That being the case, it would surprise me if we discriminate in a systemic way. For some individuals to do so unconsciously wouldn't surprise me just because it's human nature to be biased, although we do our best to unlearn that behavior.