Tennyson's line "After Many a Summer" is also the title of a book by Aldous Huxley which tells a story of someone who is able to extend his lifespan by centuries. Based on the idea that neotony is an aspect of evolution, meaning that the young of many species are livelier and cleverer than fully grown adults, he theorises that Homo Sapiens are a sort of larval ape, which is what the protagonist becomes. After many a summer he reaches maturity as a small, wrinkly white haired gorilla-ish thing.
Cheers
Dave