To add my 2 cents:
Angela Lansbury played Elvis Presley's mother (in Blue Hawaii) and Lawrence Harvey's mother (in The Manchurian Candidate). She was just shy of ten years older than Elvis at the time she played his mother, and just three years older than Harvey when she played his mother. Not to mention that, on DS, Louis Edmonds was 43 when he debuted as the 36-year-old younger brother of Liz Stoddard.
Great actors can play ALMOST any age, right?
Brian