Why in the book an elderly woman on the beach touched the genitals of a young man and looked at them.

The scene you're referring to from the book may be intended to convey themes related to voyeurism, the complexity of desire, or the contrasting perspectives between youth and aging. Such an act could symbolize an exploration of boundaries, the nature of intimacy, or the stark differences in perceptions of sexuality across different life stages. If you can provide the title of the book or more context about the characters or plot, I would be happy to analyze it further!