16 year old toddler:
http://www.newscientist.com/article/...eing-gene.html
http://abcnews.go.com/2020/Health/Story?id=7880954
She hasn't physically aged or matured since she was about a year old, though her family thinks her personality has developed some.
College student who has permanent amnesia after a bump on the noggin:
http://abcnews.go.com/Health/Story?id=7733704
She had to re-learn everything. After her amnesia set in, she retained a basic ability to talk but didn't even know how to eat.