A comment I heard a while ago is that there are now a whole load of completely new outdoor activities which are very visible and for which particpants get to wear colourful clothes: kite surfing, hang gliding, para-gliding, mountain-biking, skate-boarding, etc. and these have been taken up by some young people who might otherwise have taken up caving. The point is that caving isn't "visible" to the general public in the same way as these other new sports, and the only chance most non-cavers get to know about caving is either the few TV programmes specifically about cave exploration (though these are on the increase) or else headlines about cave rescues.
The other problem is that young teenagers are taken caving as an "outdoor activity" by schools and outdoor centres but almost always, when they approach a caving club to ask about continuing the sport, the answer has to be on the lines of "... only if one of your parents comes with you ..." because caving isn't set up to deal with child protection issues. So, although some clubs are able to help out and do accept young people, these tend to be few and far between. This then means we can't attract the really keen youngsters who we need to join caving clubs to carry on the sport and be our future.
I don't know the answer to this but the BCA Youth and Development Group is now trying to address the problem and we have a BCA Child Protection Officer who is able to give useful advice.
It's also noticeable that clubs seem to have people joining in their late teens, who are really keen but drop out after only a few years when they either get bored, having done all the longest and hardest caves in the book, or have to concentrate on earning a living. Certainly my club has had quite a number of older cavers join saying they want to come back to caving again, having done it for a while in their youth and now have time to get back to it. Those who join, or re-join, in later life seem to stick with it in a way that the keen teens didn't.