As a general rule, federal and state governments do not like any restrictions limiting who can or cannot live in a particular area, subdivision, city, etc. There are few exceptions. The feds and many states do make an exception for people 55 and over, but I know of no specific exceptions for younger age groups.
HOWEVER, if you (or someone you know) are interested in living in a 55+ development, you might check with some of these in your area. It is my understanding that the communities are allowed (at least by the feds) to advertise themselves as 55+ developments as long as 80 percent of the units are occupied by at least one person over 55. In other words, 20 percent of the units MAY be occupied by people under the age limit, though I know of no requirement that this be allowed. And your state may have additional rules about age and occupancy.
Berkshire Hathaway HomeServices.
Real Estate of the Rockies