The Argentinean writer J. L. Borges was one of the most erudite authors of the XX century. Having a broad knowledge of almost everything, he was also interested in logic and mathematics, specially in the set theory and the idea of infinitum. When he was at the funeral of his mother, who died at 99, a friend of the family commented that it was a pity that the poor woman wouldn't be able to reach the age of 100. It is told that Borges answered:
“I see, Madam, that you are a devotee of the decimal system”
Borges was right: we tend to overestimate the decimal system (based on number 10). From a vital point of view there is no much difference between 99 and 100, but for some reason, we, humans, are in love with those round numbers such as 100 or 1000. Our behavior is understandable as we normally use the the decimal system. We have 10 fingers, so it is logical our tendency to that number. Surely you have seen a child learning to add. They use their hands constantly.
But sometimes we use other numeral systems. For example, the sexagesimal system (based on number 60) is the favorite one when it comes to time. So, 1 hour equals 60 minutes instead of 10 or 100 minutes. Why? Well, we inherited the sexagesimal system from ancient cultures -Babylonians were really experts-- One important strength of the number 60 is that it has many divisors: it can be divided evenly by 1, 2, 3, 4, 6, 12, 15, 20, 30 and 60.
In addition, it is possible to count up to 60 using your hands in a simply way. Firstly, use your right hand thumb to count up to 12 (see picture below). Then, use the remaining 5 fingers of your left hand to carry how many dozens you have: 1 dozen (12), 2 dozens (24), 3 dozens (36), 4 dozens (48), and 5 dozens (60).
Anyway, I have to confess that I love both numeral systems: living healthy for 100 years (ten times ten) would not be so bad, but 120 years (two times sixty) would be superb!