It seems from survey data that happiness really does increase in one's later years, after a nadir around midlife. So aging can be a joy, and younger people - especially those reading this in their 40s - may find it reassuring.
It's more like the difference between learning to play Greensleeves on a trombone for the first time, and giving jazz solos. When you're young in life your sense of expertise comes from not being aware of your ignorance, and when you're old in life your sense of expertise comes from knowing just how far you've come. There's a joy in this that's separate from the joy of being young and having your whole life ahead of you, and it's not at all a form of resignation.