I have more confidence in the Fullfacts figures than yours Boz
The problem is that younger people are not 'joiners'. Universities have far far fewer societies for freshers to join than 40 or 50 years ago, and all sorts of voluntary organisations are shrinking or folding for the same reason.
The average age of a Conservative supporter is probably much younger than the 57 suggested by Fullfacts, and it is not the only party with that problem, both labour and LibDems have decliningmemberships, even thoigh support for the party may be buoyant.
Since part of the problem with the selection of the last 2 leaders of both major political parties has been that the candidate the parliamentary party knows would be most effective as leader of the party in parliament and on the international stage, has lost out to someone else preferred by the party membership. Surely that aspect of the election needs to be ditched, to replace it with a system that takes into account Labour voter preferences and make the decision by MPs the final part of the process. The samething applies to the Conservatives.