They must reside in your home but can be any age, Adding them to the deed would make them eligible for life, but it is something to seriously consider as they become owners and have all the rights you do.
I did add my adult kids for this purpose…but they were 23 to 31 at the time, already out of college, and into life.
APs are not yet back on sale for new purchasers due to Covid, but there really has been nothing to suggest they won’t be back in some form considering they are selling to those eligible who had passes in 2020 and continuing to let current pass holders renew.