Indeed. The FSF is a very worthy cause. If it is true there is a lack of young people involved I'd look for reasons why amongst things like "is it a pleasant space to cooperate in", "are people accepting of new people"? I never had anything to do with FSF directly, but whenever I dealt with people involved with heavily "politically charged" projects like guix, guile, linux-libre and few others in addition to very nice people I always encountered complete idiots that would try to chastise me for example for having the audacity to report problems running a nVidia gpu. Or one person told me flat out he will not answer any of my questions regarding a programming language syntax because I admitted to be making a non-Libre package for my own use. It is 100% bonkers. You may say so what, it's just one person. Every community has idiots, right? Yes, correct, but in case of these projects I had dealings with the toxicity is rather bad to the point that only very dedicated people stay. This also means the communities are tiny and it's much more difficult to get help when you're just starting out.
I think that's why we don't see many new people flocking to FSF projects.