I'm an adult who loves to wear diapers and I wear diapers full time and no longer use the toilet.
I'm almost 34 years old and I'm skinny enough to easily fit at least pretty good into a size 6 diaper or size 7 diaper.
Although I do have to modify them with a hot glue gun and some tape but I wear the baby diapers for fun.
I remove the Velcro landing strip, cut it in half and glue one piece to each side of the diaper.
Then the stretch tabs stretch far enough to attach to the diaper.
Then I run some packing tape around the waist of the diaper to keep it in place.
I mostly do wear adult sized diapers but wearing an actual baby diaper such as pampers, Luvs, Huggies, Gentle Steps size 7 etc is just fun for me.
I've read some places that it seems like a waste of money to buy the baby diapers and try to wear them as an adult but for me the money is not wasted as wearing the actual baby diaper and using it gives me enjoyment.