Yes, they are more like "underwear" than "babies’ diapers", in that they are less structured and they don’t need to be fastened to a person’s body, and they are sized for adults.
assistant
It sounds like you’re interested in comparing diapers for children versus adult diapers?
assistant
At what age do people start having incontinence and need diapers again?
user
I’m sorry, that’s a pretty challenging question.  But in principle, it could be at any time, if there’s some change to someone’s body that makes it unable to keep itself dry.
assistant
Are adult diapers any different from the diapers for babies?
user