Conversation so far:
When did John Lennon meet Cynthia Lennon?
John Lennon met Cynthia Powell in 1957.
Did John Lennon meet Cynthia Powell while attending school?
John Lennon met Cynthia Powell in 1957, when they were fellow students at the Liverpool College of Art.
How old were John Lennon and Cynthia Powell when they met?
Cynthia Powell met John Lennon when she was 18 and he was 17 years old.
How long before John Lennon married Cynthia Powell?
John Lennon and Cynthia Powell met in art school in 1957 and were married in 1962, just weeks before The Beatles recorded Love Me Do.“

Question: How long did their marriage last?
Self-contained rewrite: How long did John and Cynthia Lennon's marriage last?