Some adult communities will accept an individual at the age of 19 to be a permanent occupant of the home. As long as the first individual is at least 55 yrs.
The communities in Monroe Township where I am most familiar are more stringent, 55 for the first occupant/48 minimum for the second. Anyone not meeting the age requirement is only allowed to remain in the home 60 days. Of course those individuals that are under the age guideline's are allowed to visit and stay over at anytime. The person is not allowed to reside in the home more than 60 days (continuously). A caretaker can be under the age requirement.
I hope this answers your question.
C21 About Town Realty