And again, 55+ developments ARE retirement communities. Why can't you wrap your head around that?
While 65 may be the effective year for full Social Security, that does not mean that 65 or older is "retirement age". Many people in areas like the military, police and fire and some other government agencies can be eligible at considerably younger ages. And many people who have saved well during their work years want to retire early and do other things.
Nearly all "retirement" communities simply require at least one of a couple be over 55.