I had an eccentric aunt who had a thing about onions. Onions, she claimed, were a key food for good health. Onions nourished your blood; onions protected you from chest infections. Cut up an onion and eat it raw. How we laughed at such antediluvian fancies.
I thought of this example when I heard the children's writer Michael Morpurgo state recently that older people should visit schools to pass on their wisdom to younger generations.
Older people, said Mr Morpurgo, the author of the renowned War Horse, should be encouraged to share their family stories and transmit their memories, before it is too late. He himself got the idea of War Horse from talking to an octogenarian war veteran.
Yet Michael Morpurgo himself was 40 years of age by the time he wrote this stunningly successful story. And 40, not 14, is just about the time when you start to wonder if some of the stuff your elders were talking about might have been interesting after all.
In youth, hardly anybody is the slightest bit impressed by what elderly relations have to say, or what they remember. Youngsters may be fond of their old grandparents and other family members, and if the oldies can spin a good yarn, they may be mildly diverted. But no young person wants to heed the "wisdom" of the old. It seems irrelevant to them. The world has changed. Everything is different.
My mother made the mistake of quoting from the Book of Ecclesiastes to me when I was a teenager - "there is no new thing under the sun": to much exasperated rolling of eyes and miming of tedium on my part.
It took 35 years for me to peruse that poetic passage she had quoted from: "One generation passeth away and another generation cometh: but the earth abideth forever … that which is done is that which shall be done, and there is no new thing under the sun." There are new things aplenty under the sun, but it's amazing how life repeats itself just the same.
But young people rebuff traditionally transmitted wisdom because (a) circumstances are altered from days of yore and (b) the young want to build their own world, and cast aside what they see as the gnarled prejudices and outdated bigotry of times gone by.
And sometimes the young are right - they have a better grasp of the future they will possess than the oldies who have been overtaken by tectonic social shifts in values, not to mention technologies. If I had listened to the wisdom of the old, when I was young, I would have sought a job in a bank. In the 1960s, nothing seemed more stable, more enduring than a bank. Banks were places of utmost reliability and bankers ranked with the clergy and the police as pillars of incorruptibility. The oldies then could not have foreseen a time when all these concepts would be upended, and the words "banker bonus" a trigger for apoplectic outrage.
Oldies considered pop music trash and pop musicians ghastly upstarts with no respect for their betters. They were not to know that pop and rock music were to become globalised money-spinners and that Mr Michael Jagger would be the very epitome of the shrewd businessman whose preferred reading is the Financial Times.
The oldies will give advice based on their own experience, which is by definition out of date. It is the young who invent new ways in business, technology, science and the arts, and who understand, often intuitively, how the future will develop. Only the teenage geeks of Silicon Valley could have pioneered the extraordinary electronic revolutions we have lived through. The biopic of Mark Zuckerberg's life The Social Network accurately shows how these youthful innovators were fizzing with ideas which brought about such amazing change.
Older people aren't really fit to lecture the young on how to proceed in the world, because the young themselves understand more about the future. And you cannot really transmit the "wisdom" of life's lessons. It was Solzhenitsyn who said that every single individual has to make his or her own mistakes - nobody learns from the mistakes of others. Cycles of history repeat themselves, as do the cycles of human folly.
And as the ancient motto has it: "You can't put an old head on young shoulders". I once heard a man say that the only lesson he had learned from a long life was always to place the shower curtain inside the bath before turning on the water. Even that is obsolete now, as shower curtains disappear.
And yet, it is in old age that the unheeded wisdoms of our elders return to us anew. Just the other day a health food expert was telling me that onions are highly recommended for good health, for the blood and the pulmonary system. "Eat a raw one frequently."