But how common was it? From the list I worked from to get my ballpark numbers there were more than a few that reached age 60. It's just that a lot of people also died at age 40.

I also suspect it was not just disease caused by infectious disease that was doing these people in. Apparently if a person is subjected to poor nutrition (and even royals had that at times, like in the winter without having vitamins from fresh vegetables), working extremely hard (I mean like 14 hour days 6 days a week hard), or both it prematurely ages people. So while diseases like cancer might not be present other diseases of old age certainly would be.

If you're interested here is the list I worked up:

William I- 60 years
William II- 44 years
Henry I- 67 years
Stephen of England- 58 years
Henry II- 56 years
Richard I- 41 years
John of England- 49 years
Henry III- 65 years
Edward I- 68 years
Edward II- 43 years (murdered)
Edward III- 64 years
Edward, the Black Prince- 46 years
Richard II- 33 years (murdered)
Henry IV- 45 years
Henry V- 35 years
Henry VI- 49 years
Edward IV- 41 years
Richard III- 33 years (died in battle)
Henry VII- 52 years
Henry VIII- 55 years