This short, charming book is about philosophy, but approached from the viewpoint of a man who is questioning whether he has become old, whether he should try to stay young, whether he should be sad or glad when he does become old.
He seeks answers not only from Epicurus, Seneca, Montaigne, and many others who have pondered the questions, but also from the lives he observes on the tiny Greek island of Hydra, where he has sojourned several times throughout his life.
It's very easy and pleasurable to follow the way his thoughts develop, and I recommend you read the book so you can enjoy that.
The bit that inspired me to share this with you, here on a music-oriented website, was Klein's view on the search for spirituality which many people undertake late in life. Of course for many people this means turning to religion. But Klein notes other ways in which people "get down to serious spiritual business". He follows up a hint from Plato, who said that "pure play has intimations of the divine". He recalls a friend whose opinion of religions is scathing but whose face is transfigured when listening to music (in his case, mostly Mahler). Klein recognizes such feelings in himself when he's listening to music: "I too sometimes take off for a realm where self-consciousness and my separation from everything in the universe falls away".
I like how Klein relates this to the Zen concept of mindfulness. "A mindful person is fully engaged in what he is presently doing ... and he is ever on guard against slipping into everydayness, that is, losing full consciousness or numbing himself to it". This is a great explanation of the difference between people who keep the radio on as background accompaniment, and people who listen with their brains engaged.