How does happiness change from when someone is in their 20s to when they're in their 40s? According to a recent Atlantic article, motivation changes over the timeline of a person's life, affecting what makes that person happy and how that person expresses happiness.
One thing I must comment on is the notion that 30 years is a "long time". It's not. I can remember 30 years ago and it's frightening how fast time goes by.