Diapers do get old but diapers do not really expire or go bad.
However the plastic may degrade some on the diapers but they are most often still usable even after 15 year or so as long as they have been stored in a cool and dry climate and have not been stored in a hot or wet or damp environment.
Most diapers are used up well within a few years of being made so it's not really an issue.
The size that diapers go up to is a size 8 for baby and toddler diapers.
They also make a Youth diaper that is usually larger than the size 8 diapers for kids and teens that are too big for size 7 or size 8 diapers but too small for adult diapers.
Pampers do come in a size 7.
Pampers diapers come in size newborn and up to size 7 in their different types of pampers diapers.
Even the Luvs diapers that are also made by Pampers comes in a size 7.
Not only that but Pampers Swaddlers also now come in a size 8 which is a bit larger than the size 7 diaper and is designed to fit bigger kids.
Other brands of diapers also come in size 7 other than Pampers.
Some size 7 diaper brands are.
Cuties size 7.diapers.
Gentle Steps size 7 diapers.
Comforts size 7 diapers.
Rascal and Friends size 7 diapers.
Target Up and Up size 7 diapers.
Huggies little Movers size 7 diapers.
Huggies Snug and Dry size 7 diapers.
Parents Choice Size 7 diapers.
These size 7 diapers are designed to fit larger children who are either larger than normal toddlers or larger and older kids who may still need a diaper but are too small for adult or Youth size diapers.
Size 7 diapers can fit children from ages 4 to up to around 10 to 13 if they are skinny enough.
Cuties also makes a size 8 diaper that is called Boundless that is made for older kids who need diapers.