Welcome aboard, Kevin!
It sounds like you've experienced a
Disney Cruise Line vacation or two already and you're back for more! Much like my family, as we cannot get enough of our Disney adventures at sea. My kids have enjoyed the
Youth Clubs ever since they were tiny sailors, and now are loving the Tween and Teen clubs onboard even more.
You're correct that the Youth Clubs only go up through age 17. After that, 18 year-olds and up are welcome to attend and enjoy any of the
adult exclusive spaces onboard the ship. However, I know that at that age, hanging out with Mom and Dad isn't quite the tops of their list, and they'd like to have at least some opportunity to meet others their own ages. So, Disney has created the 1820 Society for guests who are 18-20 years old and not quite old enough to purchase alcoholic beverages, but too old for the Youth Clubs. It's not super specific on age, so if your 21 year-old wants to join in too, I'm sure he or she would be welcome, just knowing that the activities do not include adult beverages.
Check out your
Disney Cruise Line Navigator App on the first day onboard to read about when the first 1820 Society get together will take place. Be sure they attend that very first one, as it's when the Cast Members who organize it work together with the young adults to come up with activities, luncheons, specialty coffee mixology seminars, and other events. Plus, it's a good time for the young adults to meet each other and make their own plans as well. You'll then see official listings for the meet ups in your Navigator App each day, so they can plan to attend.
I hope that helps as you plan this next sailing with Captain Mickey and his crew, Kevin! Have a magical adventure!
Marcy