I have long got used to seeing policemen young enough to be my sons - but now it's the bishops! And with age develops the urge to become a spoilsport.

I mean, for instance, the staff at Mansion House here in the City of London say that of all the banquets hosted by the Lord Mayor in his year, the one for the bishops is the booziest and rowdiest. Can this really be me being slightly shocked about this - I who not so many years ago led the assembled scholars of the US Liberty Fund in a boozy chorus of Monty Python's Philosophers' Song? And it's not just the bishops who are getting younger. Five years ago I was chaplain to the Lord Mayor and I was mortified to discover that he is younger than me.

That's one of the things you do when you're approaching what Shakespeare called the "sans everything" phase: you find yourself looking closely at your contemporaries - blokes you have cheerfully ignored for the last 50 years. And you think, "Old Fred has let himself go a bit. Well at least I'm not as fat as him!" On the other hand, it's a matter of enormous comfort when you can identify someone who shows every sign of thriving when he's even older than you are. A retired banker friend of mine at 72 - a whole eight years my senior - ran the London marathon the other week.

There's another thing - the way time vanishes. It's 52 years since that Whit Saturday when I went to the Roses Match at Headingley and saw Brian Close hit 52 in 12 minutes. And I can still hear the man in the crowd - the very pitch and tone of his voice - as he called out: "Well done, Douglas Brian". And Closey himself was 75 last week. He was a god to me. Still is. But that's another thing: aren't I a bit old for hero worship?

You find it's not all decline. About a year ago I decided to do an MOT on myself and I didn't like what I saw. I had a definite paunch and the beginning of jowls. I'm Chaplain to four Livery Companies and I was eating and drinking too much at City dinners. Right then, I began a regime. The heart-warming aspect of this horrible tale is that I found after a few weeks of bends and stretches and gentle jogs and laying off the booze and puddings a bit, I could run five or six miles without getting out of breath. The weight rolled off and the cheeks de-jowled. I felt marvellous. Of course, the tendency to holier-than-thouness is a fault which certainly gets worse with age and I found myself saying to mates stuffing it away at livery banquets: "You feel much better when you're in shape, you know." Pah!

The Bishop of London gave me the parson's freehold and, as it was remarked at the time: "They can't get you out now, Peter - except for senile dementia or gross immorality". I haven't succumbed to the gross immorality bit. (To tell you the truth, I'm not quite sure I could go about it with the necessary vigour.) But the dementia is catching up with me. As another old-timer mate picturesquely put it: "The names are dropping off things." I couldn't remember what you call a breadknife the other day.

I guess one compensation for getting old is that you learn to pace yourself. As the young bull said to his dad: "Let's run across the field and (ahem!) 'make love' to a couple of those cows."

And the old bull replied: "Nay, lad, let's walk down and 'make love' to the lot of 'em."

* Peter Mullen is Rector of St Michael's, Cornhill, in the City of London, and Chaplain to the Stock Exchange.