We're not getting younger help the way we used to.
This seems to be a recurring theme in your response. I believe it, and can propose a couple different contributing factors from the perspective of a 23-y/o professional in the area:
1. The age 16-30 crowd lead extremely busy lives. Very few people are picking up new active hobbies like mountain biking in this age range.
2. It seems like almost every new person who gets into mountain biking is because their close friends, parents, or significant other is already into it.
3. CORP and the local MTB scene get almost zero exposure to the outside world. Imagine, for instance, some 22-year-old fresh college graduate from <insert favorite university> moving to Madison to work at a hypothetical large tech company in the area. How are they going to find out about the mountain biking scene in the area? In practice, they'll only find CORP if they actively go out of their way to look for it, and few people in that position have a reason to commit the extra time it takes to really get involved. IMHO, that's the crowd you want to tap into.
4. One of the biggest obstacles for young people getting into the sport is the cost of a decent mountain bike. Most people in their low 20s simply can't afford or don't want to drop $700 on a sport they don't even know if they're going to like.
I have a few ideas to bounce off you:
1. There opportunities to actively work with younger crowds. In particular, I recommend reaching out to local scout troops. When I was a boy scout in MN, for instance, I participated in a 5-night camping trip to the north shore (Grand Marais area) and spent 4 days helping build and ride about 2 miles of new trail with 50 or so other scouts - all as a volunteer effort. Only cost to the trail managers was a half dozen organizers and the hand tools. Additionally, the first feature in area 51 at camrock was an eagle scout project, for a more local example. I think coordinating community service projects like that (maybe not as big as my example though, lol) with local scout troops could help get a lot of work done in short bursts a few times a summer, while also generating more interest in the sport in the young crowd.
2. College students are extremely active will do pretty much anything to make friends. I'm not sure whether there's a Hoofer MTB Club, but if not, we should work with the union to make one, and partner with them to have 'dig-and-ride' days - we could probably get young help 2-6 times a year that way while also using that channel to self-advertise.
3. With respect to the barrier to entry of bike cost: I am not sure how to best lower this barrier, but I think partnering with local bike shops for demo days, and advertising those events would be mutually beneficial. Plus, a Hoofer alliance would be extremely beneficial in this way, because a Hoofer club might be able to keep their own fleet of loaner bikes.
These are of course just some ramblings to share my perspective as a younger person. Let me know if any of these things seem either confusing or promising.