I’ve been reading the discussion with interest. I don’t have any answers per se, but I can add some input from “younger” drivers.
Aaron and I got involved with driving during college, when we were in our early 20s. We both majored in animal science, with a focus on equine studies. One of the classes in the program was “Driving the Single Horse.” Aaron and I had the opportunity to work for the instructor, Audrey Bostwick, during the summers, traveling to Devon, the Canadian Classic, and Walnut Hill. It was a wonderful introduction to driving and I feel it started us out at the “top of the game”–we learned all the ins and outs of carriages, harness, and turnout.
We purchased our first driving pony, Coco, from Audrey after we graduated. Of course, since both Aaron and I came from an eventing background, CDE was a natural sport to try. However, we were just out of college and starting our careers; it was a huge financial undertaking.
Now, 5 years later (we are now in our late 20s) and with our 2nd driving pony, Merlin, we’ve purchased many of the things we need, but we know down the road we are looking at needing a new marathon carriage, another presentation vehicle if we move up to Advanced, etc. It is overwhelming to think about.
Here are my thoughts on what keeps “younger” people from getting involved in driving–
Amount of Knowledge Needed–Learning to ride is so easy compared to learning to drive. Not the actual skills, but the process of finding an instructor, finding the right horse (riding horses are a dime a dozen, driving horses, not so much), and getting the appropriate carriage and equipment (the options are endless and it is overwhelming when you’re not sure what you need or want). I think it is often a factor of being in the right place at the right time–finding someone who can mentor you and finding the right horse to participate with in the sport.
Logistics–Many riders are quite content with a barn that just has a riding ring. But how many drivers would be happy ONLY driving in an arena? Plus, how many arenas lack the correct footing for driving (ever tried driving in an arena designed for dressage–footing is too deep)? Also, many boarding barn don’t cater to driving horses and may not want them on the premises due to them “scaring” the other horses.
Aaron and I finally have the right set up to properly prepare for CDEs–our own farm with a grass dressage arena, access to 30 acres to drive on across the road, and access to a local horse park (15 min away) that has multiple stone dust arenas, miles and miles of trails suitable for carriages, and nice, big hills to condition on. But it’s taken us 8 years to arrive at this point.
Cost–What does an average marathon carriage cost? Typically $5-6K, and that’s on the inexpensive side. Add in quality harness (around $1K) and you’ve got a substantial investment before you even add in the horse. For a third of that, you can buy a lovely saddle and bridle, which is most more feasible for the majority of horse owners out there.
And then’s there is transportation…getting the appropriate vehicle and trailer that can handle a horse and carriage. And then, if you are CDEing, you may have another carriage and some type of ATV. It’s much easier to just load one horse in the trailer to ride and go!
Competitions–While CDEs are not terribly expensive in the scheme of things, they are cost prohibitive to those of us who are used to doing one-day horse trials or shows. I heard someone make an interesting comment at the Laurels–she said that she doesn’t understand why CDEs don’t raise their entry fees to be comparable to h/j or similar type show circuits; well CDEs could significantly raise their entries, but they would shut out all of us who can’t afford to show on the big circuits (which is why we found a new sport). It’s a catch 22.
Man Power–CDE is a sport that requires a team. You cannot do it alone, like many other horse sports. I do think it is neat how many couples get involved–the majority of our friends do this as a husband/wife team. It is a nice dynamic to the otherwise female-dominated horse world. 
That’s just the stuff off the top of my head. A few more thoughts on getting younger drivers involved–
–One, from what I see up here, there are new faces getting involved in CDEs at every show. Yes, entries are down, but I truly believe that is due to the current economic situation, not lack of interest. We certainly had to cut back this year due to finances, but we were able to work for other drivers at CDEs or volunteer.
–I don’t understand why the focus need to necessarily be on juniors or young drivers. I think it should be on drivers of all ages. Just because someone doesn’t pick up driving as a teenager, doesn’t mean that they won’t do it later on in life.
–I love the sport of CDE how it is now…down-to-earth, friendly, a lot of people competing with a horse they’ve brought along themselves. It reminds me of how eventing used to be. I agree with Thomas–growth is fine, but we need to stay true to the roots of the sport. Not change the sport to attract more people. Driving doesn’t seem to be doing this, but eventing did (short format anyone?) and it’s been a huge detriment to that sport. 
Whew! Sorry for the long-winded post.
Sure most of them will not make the upper levels, but so what? Training Level is (or should be, at least) the bread and butter of our sport.