Being technically dead, whether he knows it or not, I guess his age doesn’t matter? Based on appearances though, you can safely say he is in his mid to late teens.
He should really question a lot of things.
Sometimes he coughs up black smoke and/or has trouble breathing.
Since he’s alone a lot, he likes to play video games!
He believes his dad is around, but that’s just his memory bubble leaving things around for him.
FOOD is GREAT. He’ll make his own food, assuming his dad just magically fills his kitchen with the right ingredients. His dad always encouraged him to eat healthy.