I'm not sure clubs are anti-youngsters;
We want youngsters at our club and do have some, problem is keeping their interest when they're teenagers. We used to run a youth section and it was well attended but not one graduated to the adult section. It was before my time so I don't fully know why but it wasn't because of any resistance from the adults. Joining a club that's full of +50yr old "grandads" isn't very appealing I guess.
We strive to attract younger members (our club is free to under 16s and 50% concession for over 16s but in education), the truth is that the younger generations have been brought up with, if not fear of, certainly negative feelings towards shooting.