We are happier in old age, on average.
But some people fail to be happy in old age.
Why?
Because they simply don't learn how to age well and enjoy later life!
So, let's really nail how to be happy in later years!
WE ADAPT
Human resiliency is remarkable. We simply adapt to our new situations. Knowing that you'll adapt removes a huge source of anticipatory unhappiness - where we feel bad now that we think we'll feel bad later (humans are poor predictors of the future).
However, we also want to purposely add a huge capability to be happier. This is what we call "proactivity".
WE CAN LEARN MORE HAPPINESS TECHNIQUES
Some are automatically learned, as we tend to get wiser with age - not having unrealistic expectations and using better strategies to live life. Study the Happiness section and become an expert at happiness! Using Gratitude and especially the Reminders Notebook (and early morning review) is one of the keys.
OLD AGE IS GROSSLY MISESTIMATED AND EXAGGERATED!
The effects of older age are not really known by most people - and we as humans tend to not be able to accurately, at all, estimate either future happiness or future pain. (Read, for a perspective on how future pain is grossly misestimated: Pain About Future Pain, plus the perspectives in Pain .)
HEALTH
Read and follow You Staying Young, Roizen and Oz - Super well-done, super-informative, super-understandable.