Well I sorta did, not legally but there is a couple who call us mom and dad. They treat me like I was their mother. One day a silly twit of a young woman told the daughter by choice that she looked like me, and that her husband looked like "dad". The daughter told her "fool! I didn't marry my brother". I laugh and tell them that they were such good babies I didn't even know they were around. They adopted me as Mom because I treated them better than their real parents did. They are great 'children' because I didn't have to raise them! So sure I would adopt an adult if an adult really needed adopting.