Two views of the relationship of happiness and aging:
This article from The Economist describes how happiness dips during the middle years of life but then trends back up in later years.
This video from TED provides one possible explanation for the dip. I appreciate the comment within it that we sometimes think of happiness as a binary function — either we are happy or we are not — while it is more useful to think of it as a continuum — kind of like the 0 to 10 pain scale hospitals use.
Finally, something to look forward to. . .