I think it's been observed by many psychology studies that conscientiousness (the personality trait that determines self discipline and self control) tends to increase with age. Excerpt from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2562318/:
"Agreeableness demonstrated a fairly linear increase with age whereas the pattern for Conscientiousness was curvilinear: scores increased up to a peak somewhere between the ages of 50 to 70 and then declined."
"Agreeableness demonstrated a fairly linear increase with age whereas the pattern for Conscientiousness was curvilinear: scores increased up to a peak somewhere between the ages of 50 to 70 and then declined."