There have been 12 monarchs of 'Great Britain and the United Kingdom' since it was formed with the merger of the Kingdoms of England and Scotland in 1707. Most of these were long-lived. They were all in the job for life, with the exception of George III who was stood down on account of his insanity, and Edward VIII who abdicated because he wanted to marry a divorced woman.
In terms of age, our present Queen Elizabeth II is out in front and still there at 83, before her, Queen Victoria lived to the age of 82, George II to 77, William IV to 72, George V to 71, Edward VII to 69 and George IV to 68. I suppose it could be argued that these men and women led pampered and privileged lives, which could explain their longevity in past times, when life for most ordinary people was hard, poor and relatively short.
Like the members of the House of Lords, our monarchs too, are unelected and therefore undemocratic. We had an elective monarchy in Anglo-Saxon England, from the 7th to the 11th centuries and election means that, in theory, you can choose the right person for the job. From the political point of view the greatest asset in having an hereditary monarch is that they can be prepared for their constitutional role from a very young age.
The greatest asset in having a monarch at all is explained by the word 'experience' Queen Elizabeth meets with her incumbent Prime Minister on a regular basis. Since her coronation in 1953 she has met with Churchill, Eden, Macmillan, Douglas-Home, Wilson, Heath, Wilson again, Callaghan, Thatcher, Major, Blair and now Brown. So Gordon Brown 'might be' and no doubt 'is' given advice by a woman who, to some extent, has seen it all before - eleven times before. There must be some virtue in that.