"My plea is especially to the ‘younger’ ones – that is anyone under 55"
Now I'm just depressed....
. Officially over the hill.
But seriously I agree with everything you say and do 'my bit' for our village garden club which, happily, can still get 50 people through the door some months but even in my now officially advanced years (no I'm not 60 for some time to come), I'm probably the second youngest member of the club. Our local AGS group is much the same.
I do know, however, that the modern pressures of working life do limit enthusiasm, and time, for extra curricular activities and that's from someone who hasn't had to raise children.
Solution.....alas I haven't got one except to keep trying.