If it’s true then this is a propensity and not a rule.

My mood in college was suicidal. My mood by my 30s was better than most people I’ve ever met (sans hiccup from a year of no sleep with a newborn).

Looking back my horrible mood in college was probably caused by isolation, no sleep, high pressure course load, and too much alcohol. And I’ve noticed my mood drops dramatically when I get it in my head that I need to be more successful, at any point in my life.