Who says you're never too old to be a father?

It isn't fame and fortune you need when you're bringing up children, it's stamina and energy

Fifty-seven is nothing. A friend of mine has just become a father at 72. So if Ken Livingston, beleaguered mayor of London, is worrying about the wear and tear on his nerves, his sleep and his general help with a new baby expected in December, he can relax and get back to sorting out the bus lanes. Why, compared to Sergio, my septuagenarian friend, he is scarcely more than a boy himself.

It's the babies I feel sorry for: Ken Junior and Piccolo Giuseppi, whose father by the way isn't strictly my friend. The connection is his wife Diana – I can't remember if she's his fourth or fifth wife – who've I've known on and off for years. Why on earth is Diana marrying a 70-year-old Italian? I said when I heard the news. Silly question. Why does anyone marry a 70-year-old – anyone at least, outside the pages of a Gabriel Garcia Marquez novel. Sergio isn't just rich, he's mega-rich. Something to do with plumbing I believe. Italians are crazy about plumbing. We stayed in a hotel on Lake Orta one summer where, instead of shoes and scarves and jewellery that glass cases on the hotel lobbies usually display, these were full of bathroom taps.

So why, you wonder, do I feel sorry for a kid who's going to inherit a plumbing fortune and another whose father (I'm sticking my neck out here) will one day join Dick Whittington and Rudi Giuliani in the mayoral league tables? Because it's not fame and fortune you need when you're bringing up children, it's stamina and energy and the ability to score from a bicycle kick straight into the back of the net or at least have a bash at it – in a nutshell, it's youth that counts where raising children is concerned.

I speak from experience. Sixteen years separate my oldest from my youngest child and I have absolutely no doubt that the older ones got better value from me in terms of maternal skills, attention, adventures, bedtime stories – and even better food – than the unfortunate tailenders. When my older children were small we went on all-day bike rides, the youngest in a child seat behind my saddle, the basket attached to the handlebars full of the cakes we'd spent the morning baking. We would cover 20 or more miles, come home, play games in the garden, I'd make shepherd's pie, give them all baths and eventually get them to bed when I'd sit down for half an hour at least and continue with the story I'd been telling them.

Yes, telling not reading. They insisted on spontaneous original narratives about princesses and goblins and polar bears and God help me if they spotted any repetition, hesitation or deviation. Those were the days when I had sufficient energy to win arguments about not leaving the table until they finished all their vegetables and how much television they should watch and what time they should go to bed. As you get older you compromise. By 7pm all you want to do is listen to The Archers and go to bed. Well, why not send out for pizzas if that's what they want. Okay, let them watch television, at least it saves me thinking up stories.

Is it fair to have kids when you're old? I once spent an entire afternoon consoling a mother who had been mistaken by the teacher for her daughter's grandmother when she went to pick her up from school. She could have been. She was 48, she told me, when she had Samantha. She and her husband had been trying for a baby for 25 years and were naturally ecstatic when Samantha arrived. Now she wasn't so sure. Samantha had asked if she could come home by bus.

One of the strangest father-son relationships I ever encountered was at a Sunday lunch in Wiltshire, with friends of friends. I don't know exactly how old the father was -- he certainly looked well into his 70s, especially without his clothes on (we went swimming after lunch). But he insisted on his three small sons calling him, sir. We played that energetic ball game called Marco Polo in the pool and the father, alias Soames Forsyte, to his credit joined in despite his frail physique. "Oh Sir, please sir, over here sir,'' his sons would shout as their aged father, clutching the polo ball like a life rope. clung to the steps of the shallow end.

I don't for one moment suggest that Red Ken will take such a stuffy attitude to fatherhood. But time, quality time, isn't on his side and he if wants to cut the mustard as a hands-on dad he'd better get down to the gym.