As a 65 year old, I might argue that my mental faculties have changed, not necessarily lessened. I can't juggle 5 mental balls anymore, but I just write down what I need which is probably better.

I play poker with some 90 year old's, and they are damn sharp. Some people get dimmer with age, many continue to shine.

Getting a degree is a more traditional route, which older people tend to pursue. But he might be doing it for show partly since he is a politician.