Why is it that most nudists are middle aged or older? Several reasons... Their kids are more often out of the house and they have more time and money. But I think the bigger reason is that as you get older, you're less likely to accept stupidities in the culture which don't make sense and are often destructive (discrimination, barriers of class or position, etc.). And you're looking for a little diversity in your life. Maybe you travel more or make friends with someone from outside your cultural or religious background.
That's not to say that many young adults aren't open-minded. But they are less self-confident about doing things which might not be accepted by their peers or "superiors". That said, when nude beaches are available near colleges, you'll often find them dominated by students and faculty. Often a travel club will form in the area where a good percentage of the members are young adults. Such is the case near Wreck Beach near Vancouver and Mazo Beach in Wisconsin. And at some clubs, you'll find more young adults and young families, then at other clubs. Encourage them to travel to Europe and Australia, and they'll see how much more closed minded Americans are about nudity.
What can be done to prevent the youth from being so close minded (clothing compulsive)? As a culture, let's bring back the open showers in school and have the kids use them as they should....naked. It builds self-confidence and acceptance that the kids lack these days. Have more beaches and public lands where people know they have the option to not have to wear clothing if they don't want to. Encourage more festivals like Burning Man, where you can be naked the whole time if you want to be. Do so while attending them, and encourage others to do likewise.
Start travel clubs near college towns and actively recruit at the colleges. Hold info sessions, both on and off campus. Fight to have nudism and body-freedom be acceptable topics for student social life. Campgrounds and resorts near such places should advertise heavily and offer student discounts. Offer a free weekend for selected student organizations to come and see what it's all about. The majority of students should know at least that your organization exists and that it's worthy of consideration.
The internet does a good job of communicating and raising awareness, but nothing beats someone talking to a real person at a short info session, answering real questions, as they come up.
I came to it by self-discovery and curiosity in my teen years, and I started to explore what it was about soon after getting out of college. We can continue to dream about changing the culture, but we really do need to offer alternatives to the kids when they are most receptive. In college and in the early adult years before they get set in their ways and being to pass on and intensify the self shaming behavior to the next generation.