SuperGrandpa was the very first character of the full concept of FamDoodily. We imagine grandpa (and we are sure that we are not the only ones) as a Superhero, and we decided to make a real hero from him. This is why he is wearing a shirt with his logo with the G in the middle.
Maybe there are sometimes some funny situations in which ones you would imagine your grandparents as little children. This is the reason why SuperGrandpa appears at most in ‘Forever Young’ series together with FairyGrandma. ‘Forever Young’ won’t be the only story where Grandpa will appear, of course!