Pampers size 7 would unlikely fit a teen.
If the teen needs to wear diapers then they can wear Youth sized disposable diapers that you can buy online.
A really skinny teenager may be able to squeeze into the Pampers size 7 diapers but it would be a tight fit likely and would likely not be very comfortable.
You could try fitting into a size 7 diaper as my 8 year old fit into them pretty good and seemed to have a bit more room to grow into them.
However a teen would fit much better and be more comfortable wearing either an adult disposable diaper or a Youth disposable diaper.
You can buy Attends Youth Disposable diapers or Attends Adult Disposable Diapers.
Or any other brands of adult diapers or Youth Diapers are available.