Maybe? The type of diversity that companies care about (to contrast with the many strawmen out there) happens to be good for the bottom line. That is, a team with 5 men and 5 women is likelier to perform better than one with 10 men [1]. Some explanations I have heard are that diversity brings perspective that wouldn't be present in a monoculture, and that it improves psychological safety which is a huge determiner of team performance [2]. There are models out there made by actual social scientists of why diversity helps. See [3] for instance, has both elements.
It does seem like age-based discrimination would have a negative effect on psychological safety, as with any discrimination due to conscious or unconscious biases. Regarding perspective, an experienced individual could either bring in valuable insight from their experience or constantly veer towards the status quo, partly depending on how you want to look at it.
I think the answer is: it is complicated. You now have my ideas on why diversity is valuable. Does age fit that model? (Even if not, of course, age-based discrimination is not good.)
[1] https://news.mit.edu/2014/workplace-diversity-can-help-botto...
[2] http://www.nytimes.com/2016/02/28/magazine/what-google-learn...
[3] https://hbr.org/2013/12/how-diversity-can-drive-innovation
[4] https://www.fastcompany.com/1841060/redefining-diversity-new... - bonus