The happiness of old age is a good illustration of the fallacy of our culture's normal view of happiness.
We fear old age because we see it as a process of loss, of having to let go of things which we depend on for our well-being. But it's this very process which actually causes the well-being of our later years.
This process of letting go brings a new authenticity. It brings them into contact with their "core selves", the essence which was obscured by all of these attachments.
Now that they're no longer focussed on finding happiness outside themselves, they begin to find it inside. They begin to realise that they don't actually need external things for their happiness, and find a natural contentment in simply being.
*