The most dramatic example I know of someone who is older and also not a well known who found a major result is Kurt Heegner. He was a 59 year old private tutor and radio engineer with no previous published results when he proved the Class Number 1 problem. His proof was initially rejected by the mathematical establishment and he died before learning that the proof was a major advance and essentially correct.

http://en.wikipedia.org/wiki/Stark%E2%80%93Heegner_theorem

This story and Heegner's are particularly interesting because over the years some prominent mathematicians have stated that they believe mathematical creative declines rapidly with age.