'No one waits at bus stops,' the middle one says, making his durrrhh face without looking up from the television. 'You just use the bus app'

I've been going to the gym twice a week, early in the morning, for about 10 years. In principle this means I maintain a minimum level of fitness that enables me to sit at a desk in front of a screen for long periods of time. In practice, it means that I am always in at least a little bit of pain.

"You're back early," my wife says when I come in with my bike, a few minutes after eight.

"I got sent home," I say.

"For what?" she says.

"For hurting my neck."

"Oh dear," she says.

Neither of us has much patience with the other's infirmities, and my largely invisible complaints do not interest my wife at all. Over the course of the day, my neck loosens up, but tendrils of stiffness spread throughout my back. The next morning I am woken by a startling ache in my left leg. I limp downstairs to find two of my children sitting in their school uniforms, watching TV in the dark. The floor is freezing under my bare feet.

"It's cold out there," I say, looking out of the window at the frosted cars. "You'd better wear hats."

"We don't have hats," the youngest one says, rolling his eyes.

"How can you wait at a freezing bus stop without a hat?" I say. The very thought makes me shudder.

"No one waits at bus stops," the middle one says, making his durrrhh face without looking up from the television.

"Why not?" I say.

"You just use the bus app."

"The what?"

"Next Bus London," the youngest one says, waving his phone at me.

"You wait until it says three minutes," the middle one says, "and then run down the road."

For some reason, I am completely taken aback by this. My leg throbs. I went to sleep middle-aged, I think, and I woke up old.

At about midday I come downstairs, wearing one cardigan over another, to find on the mat a letter from my 90-year-old father. He writes to me, on average, once every five years, but I recognise his spidery hand from several paces. The letter inside is a single sheet of yellow lined paper, pulled from the notebook he keeps by the phone for messages. I wonder what might have prompted this latest outpouring, until I recall that my sister and her husband, who live with my father, have gone on holiday to Australia.

"It's boring here alone," my father writes, "so I thought I would see if I could remember enough to write a letter."

My wife comes into the kitchen. "What's that?" she asks.

"A letter from my dad. He says my brother tried to poison him with a tainted chicken."

My father's subsequent attempt to cook for himself did not go much better. "Sparks started to fly out, so I turned the stove off," he writes. "Unfortunately, it kept right on burning, so I sat down to watch the display. When it finally burned out, I watched for another half-hour to make sure. If I burned the house down, they'd try to put me in a home." I check the envelope to see when this cry for help was postmarked.

"How is your back?" my wife asks. "Better?"

"It was better," I say, "but now it's my leg. The pain seems to be travelling down my left…"

"Please don't tell me. Does your father say anything else?"

"He says, 'PS – I used lined paper so it wouldn't look like a cardiograph.'"

"You should write back," she says.

"I will," I say. "I'm going to tell him my leg hurts."

Actually, I think, I'll tell him about the bus app. It will blow his mind.