There is a lot of competition from outdoor activities for any interested youngster. Tens of thousands each year get to try caving as an instructed trip usually through school, outdoor activity centres, scouts, cadets etc. A small number will be attracted to the sport of caving but there are numerous barriers to participation for them. I suspect it is far too easy for them to be sidetracked into a different activity which is simpler to participate in. If they do get to uni, and that uni has a caving club, then that early interest may attract them to join, but not everyone goes to uni and not all unis have a caving club, and of course by that time the interest may be lost. Ideas such as the adventure academy are needed to address this element of early participation capture but that needs rolling out across the country supported by a huge volunteer resource that is where it will likely struggle.
I find it interesting that a few under 18s that I have known have become very competent cavers at quite an early age, even to the point of doing British grade fives and major European caves with ease. However, all of these have had caving parents or guardians. There must be huge potential in youth caving which is seldom realised.
Anyway I appreciate I am answering a question about young cavers on a thread entitled 'old cavers'. Apologies to the OP