Kid asks his grandfather if he can have one of his beers...

The grandfather looks down at the 10 year old boy, and asks him, "well, can your dick reach your asshole?"

The boy shuffled and made a discreet attempt, but realized it was futile, and replied, "no"

"Then no, you can't"

3 years later, the boy finds his grandfather drinking again, and again he asks if he can have a beer.

"Can you dick reach your asshole?"

"No."

"Then no, you can't have a beer."

3 more years later, the boy, now 16, confidently walks into the garage to find his grandfather drinking again. He smiles and says, "Grandpa, can I have a beer?"

"Well, can your dick reach your asshole?"

"Yes," The boy replied, grinning.

"Good, then go fuck yourself!"