Well, the 18-25 crowd is busy with school.... and school is expensive
and time consuming. After that, they are working, trying to get
"grounded" as an adult, buy a home, get married, this sort of thing.
Then perhaps kids... and only when the child is old enough to not need
constant attention, and they have financially recovered from all of
the diapers, pre-school and daycare fees, etc, is there time for
something other than parenting... thus the 35 crowd.

This is where I sit, I wasn't able to start flying until recently, at
37, despite having an interest in flying since age 16.

Incidentally, I didn't start sailing until about the same time,
despite an interest in that also.

-tom