Spencer was a 500cc world champion at 21, which was the youngest at the time (early 80's?) and in 85 I think it was he won both the 500 and the 250 world championships, both in the same year. I don't know if anyone has done that besides him?
"The atoms or elementary particles themselves are not real; they form a world of potentialities or possibilities rather than one of things or facts."
- Werner Heisenburg