There is no widely accepted answer. This is one of the big open questions that quantum mechanics is still trying to figure out, and different interpretations have put forward various answers.

https://en.wikipedia.org/wiki/Observer_(quantum_physics)

There was a graph yesterday showing the average age of Senators over time, which in particular showed that Senators have gotten a lot older in the last 50 years. This is essentially showing that the average age of the Senate is basically just following general demographic trends in the US.