Research has shown that happiness in older years is generally higher. In a 2014 study conducted by English and Carstensen (see reference below), older adults reported more positive emotions in low arousal positive emotions (low arousal states are defined as: happy, content, calm relaxed) during the entire day vs. younger adults. Younger participants felt more negative in the evening.
There was little age difference in those who were in high arousal negative emotions (high arousal negative states were defined as: anger, anxiety or sadness).
Figures from the Engilsh and Carstensen article referenced below.
So the research does seem to support that “we are more mellow as we age”. Think about your emotions, are you happier in the morning or evening? Are you happier than you were when you were younger? It good to be us, isn’t it?