1
general::
Phrase(s): a ripe old age
a very old age. • Mr. Smith died last night, but he lived to a ripe old age—99. • All the Smiths seem to reach a ripe old age.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
An age advanced in years, as in I expect to live to a ripe old age. The adjective ripe here means "fully developed physically and mentally," but the current use of the idiom usually just signifies a long lifespan. [Second half of 1300s]
American Heritage Idioms