Some random trivia for you. I was curious to see what percentage of people had known only one monarch in their lives. Here are some very rough figures that give an approximation.
As of today, the Queen's been reigning 66 years and 209 days.
According to the Australian Bureau of Statistics, on June 30 2016 (when the Queen had reigned 64 years and 4 months), 15.3% of Aussies were aged 65 and over, so 84.7% have only known one monarch.
http://www.abs.gov.au/AUSSTATS/abs@.nsf/Previousproducts/3101.0Feature Article1Jun 2016
Also as of 2016, 18% of Brits were aged 65 and over so roughly 82% have only known one monarch.
https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationestimates/articles/overviewoftheukpopulation/july2017
Of course, this doesn't account for all the people who have died in the last two years, etc, but it gives a bit of an idea.