The term "Senate" comes from the Latin word "senex" meaning "old man", and obviously the US inherited the term "Senate" from ancient Rome. This is a basic structure of society.

The issue is that this particular group of people older than 65 at this particular time in world history (which you happen to be living in) are Boomers who are probably the most child-like, foolish, and ignorant generation of people in world history, due to the circumstances of their upbringing (post-WW2, high technology, opulence, drug use, sexual revolution, peace in the developed world).

This isn't ageism, since normally old people do tend to have more wisdom and knowledge than young people.

There is something that really went wrong with the Boomer generation. The goal of every society is basically to survive their Boomer generation which many are not really seeming to manage.