Picking Up The Tab

My friend and mentor, Ken tells me that there is an old Spanish proverb (and it rhymes, so don't complain):

Cuando hay barbas mayores,
no pagan los menores.

Roughly translated: When there are old guys, the young folks don't pay.

Happily, Ken is older than I am. And he has a bottle of Spanish brandy.

When do you pick up the tab?