Research says that skills concerning self-control increase with age.
This experiment shows that children have trouble delaying

I really wonder whether it is true that delaying gratification is a
function of age. My roommate tells me every Monday that next weekend
he will stay away from heavy partying. And then, at the end of the
week he is off partying until Sunday whereafter he tells me that he
shouldn’t have stayed out all night.

So here is a question for you: Can cognitive skills be trained? If
yes, do you have suggestions for training my roommate?