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.
If a girl has a desire to be a slut, who but her father should help her? Especially since such girls are successful in male society. And can a daddy be against his daughter's happiness?