And why would the grandfather resist? When else would he have such an opportunity. Besides, it's always easier with a temperamental woman - she gets herself turned on and therefore comes much faster. You would have tried to bring to orgasm phlegmatic fat girl with a huge hollow. That's the kind of woman you should run away from. I've been in the middle of one of those, you can't wish it on the enemy.
How all the girls love young tutors, they apparently drool at the sight of these men with pumped arms, so they give him all the passion, in principle, not surprised.