How does the author present the paradox of aging in the novel, Love, Again?

In context, Sarah's love for Bill (twenty years her junior), is doomed from the beginning, but that does not stop Sarah Durham from experiencing all the agonies and delights of love, as if she were not sixty-five years old but a girl of eighteen. Indeed, one of the ideas in Love, Again is the paradox of ageing: the fact that the passions and yearnings of youth can live on like an eternal flame while the body slowly declines. As Lessing puts it, "The flesh withers around an unchanged core."