I have zero problems with the age gap or senior's soul in a young guy's body trope as a lot of people seem to have. What I can't get passed is the fact that the grandfather stole (accidentally or not) his grandson's body and life and as a bonus gets his grandson's love interests. I'd be more open if say the grandfather was a retired gangster who finds himself in the body of some random high schooler after performing a heroic deed. I don't know. Something like that.