"I don't think," said my father-in-law from his hospital bed, "that I can go back to the classroom. Perhaps you could contact the school and tell them I'm retiring."
"Yes, well, that sounds like a good idea," I replied, "given that you're 94 years old."
"Am I?" he said with amazement. "Are you sure about that?"
He had been admitted a few days earlier suffering from infection-related delusions, so perhaps it wasn't altogether a surprise that he thought he was living in 1981, his actual date of retirement from teaching.
A few days after this exchange, I came across an article in the London Evening Standard headlined "School's not out for older teachers". With a rising school-age population and so many teachers retiring early, the fear was that the system would struggle without them.
To illustrate the piece, the Standard had chosen a picture of a kindly old chap with a white beard and a benevolent smile. He was sitting cross-legged on the carpet, surrounded by expectant nine-year-olds, clutching a story book from which he was about to read.
Immediately two questions came to mind. The first of which was: how's he ever going to get up from there? The second, more seriously, was: how old is too old for a teacher?
The answer was easy enough before ageism came to sit alongside racism and sexism as one of the great no-nos of our age. Once you reached 65 you were obliged to head off for wing-back-chair-land and forget you ever had a brain. As a 66-year-old still happily in harness, you might say, "he would say that, wouldn't he?"
But of course it's not just me hanging on in there now that competence and personal choice is the deciding issue rather than simple chronology.
And surely the only answer to "how old is too old?" is that there is no answer. Or, at least, there is no one-size-fits-all solution. Some teachers know that they've given their all well before they hit 60. Others - if they can set things up in a way that suits them - can push on with gusto for a decade or even more.
The thought of going back to five days a week - and in reality that means six or, sometimes, seven days a week - fills me with horror. But knowing that I can leave the worst of the admin to others and just go in and teach can still get me out of bed in the morning with a smile on my face.
Interestingly, my nonagenarian father-in-law was a bit of a pioneer in this himself. After his retirement from primary school teaching he went into adult education, teaching history and art history to access students for anything up to 15 hours a week. When he finally called it a day, in his early eighties, he was still being asked by his manager - and his students - to give it just one more year.
So maybe there is an answer to the question after all. Despite having his intellect largely intact, my father-in-law realises that with almost no vision and only about a quarter of his hearing left, perhaps 94 is just a little too old for the classroom.
Stephen Jones is a lecturer at a further education college in London