An individual can easily remain capable into late age, but it's not evidence of age discrimination if mostly young people work at/apply to some positions. Here's some evidence of cognitive decline: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2683339/
Skimming, that is an interesting article. I feel more productive in my newfound dotage than I was in my twenties. Nevertheless I suppose the data don't lie, do they? Or mislead?
> Results from three methods of estimating retest effects in this project,... converge on a conclusion that some aspects of age-related cognitive decline begin in healthy educated adults when they are in their 20s and 30s.
If you (and I hope you do) live well beyond your 20s and 30s I hope you'll remember that getting fucked by ageism is real and unavoidable if you work for the man in this industry.