An 8 year old should wear diapers all the time if they want too or need too.
Diapers are made for all ages and many 8 year old boys wear diapers all the time or at night.
Diapers are the better underwear anyway and are more comfortable.
I have an 8 year old son that also wears diapers all the time as he's not potty trained and he's not interested and wants to wear diapers.
I think he's cute in his diapers and he can use diaper and wear diapers all the time.
This picture is of another kid but my son looks about like him and wears just his diaper like the boy below who is about his age.
More of his pictures can be found at the link below.