The play has weathered well, with the quickfire Paisley patter of the boys in the carpet dye factory as entertaining as ever. However, what caught my eye was the audience. They had a vaguely familiar look about them, and I realised, with a shock, that they were probably the same people I had sat with in the Bedlam Theatre in 1978, watching the same play.
There was a similarity about them that was quite noticeable: the 501 denims, the receding hairlines (Pots and kettles here! Ed), the extra pounds - in wallets and in weight. I was reminded of the memorable line from Field of Dreams: "My God - you're from the Sixties!" What I couldn't understand was why they all looked so old.
Arriving in school next day was the latest missive from headquarters inviting staff over 50 to enquire after early retirement packages. I wondered why it was in my pigeonhole, before succumbing to the obvious. The problem with being part of an ageing profession is that tempus tends to fugit almost imperceptibly. Like most staffrooms these days, I suppose, ours is a mixture of greybeards and fresh-faced probationers, with few in between. It feeds the delusion that the 1980s were only a couple of years ago and nothing much has really changed.
It's the same at home, where the wailing of my son's electric guitar is indicative of yet another 1970s anthem that he is seeking to master.
Cranking up the television volume to drown out the noise, I realise that we are tuned to UK Gold, in one of its many guises, and can look forward to an evening's viewing that includes Bergerac and The Forsyte Saga.
It's a kind of digital dementia - and I wouldn't be surprised to see a Z-car outside, or to phone a local company and hear a local accent.
The mirror does not lie, however, and preparing for our end of term festivities for the 27th time, I'm forced to admit that, although the staff panto jokes haven't changed much, this writer certainly has, and there is a limit to how many more Christmases I'll be celebrating within the warmth of a school community.
It could get you down, but I prefer to use it as a launchpad to recapture my youthful enthusiasm and make the most of it all. But, in the background, the wise words of forever young Doris Day echo through the carols: "The only bad thing about middle age is that you grow out of it."