Nothing. Its a social thing. People forget that there are issues that some adults and older children have which require protection from "accidents". There are thousands of people who require this type of protection to allow them and in some cases their carers to have as normal a life as possible. There really isn't anything wrong with wearing this type of product if there are circumstances demanding it, its just the way people think and behave when they hear of others wearing them that is an issue.
There are several fictional stories and fan-fiction pieces that feature teenagers wearing diapers, often as part of a specific kink or fetish scenario. It's important to remember that these are fictional and not representative of mainstream teenage experiences.
It is not normal for teenagers to wear diapers if they don't have a medical issue.
The overwhelming majority of teenagers don't love to wear diapers. Why a few would prefer to do that you'd have to ask them.
== == Answer I don't understand why, every time this is brought up, everyone always has to say that you need counseling, like your mentally unfit to walk outside your house. The only Problem with wearing diapers is if your living with someone you love, and he/she isn't very comfortable with it. There are Lot of people out there who enjoy wearing diapers, and there is nothing wrong with them.
I would say approximately by the age of three or four. It depends. I could be wrong though.
A surprising number of people are "into" wearing diapers. It's a harmless sexual interest -- enjoy yourself!
Copy and paste this: http://www.bing.com/images/search?q=Adults+wearing+diapers&qpvt=Adults+wearing+diapers&FORM=IGRE#view=detail&id=651F4FF17D6242597BFED55DD1E34E5E35630CCA&selectedIndex=7
you dont
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Teens do not go out wearing diapers without pants. In fact, many teens do not wear diapers unless they are suffering from a mental disability.
Generally, teens do not have a widespread preference for wearing used baby diapers. Most teenagers view diapers as items meant for infants and may find them uncomfortable or socially unacceptable. However, there are niche communities where some individuals may have specific interests or fetishes related to diapers. Overall, this is not a common trend among the majority of teens.
There are online suppliers of diapers that will fit teenagers, just search on Google or another search engine.