Wow - this thread really does get to the heart of the matter around target market. So easy to get into stereotypes without realising it.
I suspect the age demographic is much wider than is indicated on this or any other similar forum. I reckon it’s more likely, though, that the older (crappy term I know) members are less likely to engage fully, or even at all, in expressing their views. They’re probably just getting on with the Monzo experience in whatever way works for them.
For them, maybe, the cut and thrust, such as occurs from time to time here is too tiring to bother with.
At the risk of upsetting some (though I’m sure I won’t 
) perish the thought that the startup banks’ forums become the places for youthful banter alone - cos that’ll be one boring place to be.