Ever since the Arabs invented zero some 12 centuries ago, we have been mesmerised by numbers ending in that digit. But, for some curious reason, we attach importance to dividing figures such as 100 or 1,000 by the figure four - so that, for example, we attach particular significance to figures such as 25, 50 and 75.
Yesterday, I was a beneficiary of this apparent anomaly, because people have made a particular fuss about my 75th birthday. I'm not complaining but I am mildly puzzled by it. But then I'm equally puzzled by the concept of compulsory retirement at 65.
Of course I understand, and am personally very grateful for, the idea of retirement pensions, a concept that we owe to Chancellor Bismarck, who in 1889 persuaded Emperor Wilhelm II of Germany to propose to the Reichstag the introduction of old-age pensions at age 70.
In Germany, this pension age was reduced to 65 in 1916, in the middle of the Great War. And, shortly before that, the old-age pension system that we in Ireland now enjoy had been introduced by a British chancellor, David Lloyd George.
If I may temporarily divert from my retirement theme for a few paragraphs, I would like to point out that by taking this step the man who was later to negotiate that Anglo-Irish Agreement of 1921 - popularly known as "the Treaty" - had, possibly without realising it, reversed the earlier net flow of resources out of Ireland to Britain.
That outflow had been estimated by a British Royal Commission in the 1890s to have involved some £300 million - perhaps £30 billion in today's money - from the poorer to the richer island during the 19th century. That was because in those days taxation tended to be spent centrally on administration and defence rather than spread around for welfare purposes.
I have often wondered what would have happened to this part of Ireland if the issue of Irish independence had been postponed until a time when, with the further expansion of social welfare, the loss of net transfers from Britain would have cost us between £5 to £10 billion annually in today's money terms. If we had remained in the UK much longer, would we ever have felt able to take the huge short-term financial loss that would have come with independence?
WHAT hope would we have had of creating a viable and prosperous economy if we had remained in the UK - given that our much weaker economy would have become ever more dependent on British transfers?
But back to pensions: the provision of pensions for those who retire does not necessarily entail enforcing a compulsory retirement age.
When I recently looked up "retirement age" in an encyclopedia I found no reference to the origins of the idea of a compulsory retirement age.
Whence came the idea that people should, regardless of their capacity, be required to retire from many employments at 65 - or at an earlier age in the case of women? Was this a British civil service rule we inherited, then extended to other occupations? A fixed, compulsory retirement age is essentially arbitrary, for people's capacity to remain productive does not suddenly end magically at 65. For some people that point comes earlier, and for others much later.
We know that in 1991 close to half of men either retired before 60 or else stayed on working after 65. And, as many of the remainder must have stopped work between the ages of 60 and 64, it is clear that only a minority of men retired at 65.
As people's lifespans increase, does it make any sense to continue to impose a retirement age which seems to have been arbitrarily fixed in the last century?
Given the changing health conditions of the past century, the effect of having such a fixed retirement age has been to increase hugely the proportion of the average person's lifespan that is spent in a condition of dependency - either in education or in retirement - and thus to impose an increasingly heavy burden on the declining proportion of the population which is working.
For my part, I find the concept of retirement elusive. I suppose I could be said to have retired a number of times - from Aer Lingus when I was 32; from running an economic consultancy when I was 46; from academic life at 47; from being a cabinet minister at 51; from being Taoiseach and party leader at 61; and from the Dail at 66. But these were not really retirements - they were simply career changes. No, I'm afraid if I actually retired from work, I might turn out to be one of those who are unable to survive retirement - and I don't intend to take that risk.
gfitzgerald@irish-times.ie