I’ve got my free bus pass 
The idea is that we are tried by “a jury of our peers”, our equals.
Maybe us oldies are less tolerant…
Exactly so. 
Having a range on a jury; older to younger, self-employed to professional to manual worker, to unemployed, male/female gives a better chance of a balanced view when discussing a case and reaching a verdict.
It never will be perfect but better to have a range than just, for instance, middle class blue rinse matrons who want to stop the young beatniks in their area from frightening their pussies.
Don’t get a hungry judge in the USA, as that can affect the outcome of the sentencing ,or if he or she wants an finish in the afternoon for a round of golf, and the daily cases have been delayed.
I pass no comment what the Judges get up to!
What happens in private chambers, stays in private chambers.