For a start, my 17-year-old daughter keeps shopping for 'vintage' clothes in charity shops. These turn out to be the back-of-the-wardrobe cast-offs of a woman roughly my age.
Secondly, teenagers look totally unchanged by late nights. Their eyes are bright. Their skin looks dewy. They look as if they could carry on for several more days without sleep.
Generally, if I've been up past midnight, I look like a deflated balloon covered in a fine layer of dust.
Thirdly, teenagers play music you liked yourself when you were young. This is because it's become so old-fashioned it's acquired the shiny new sheen of retro glamour.
Blondie, for example. I remember boys my age going all glassy-eyed when they looked at pictures of Debbie Harry. I can't believe they still do.
And, as a final insult, teenagers repeat back your requests with incredulity, as if you've suddenly aged by fifty years and can't think beyond woolly blankets and cups of cocoa.
"Will you be warm enough?" I say to my son who is about to venture out into sub-zero temperatures in a thin white T-shirt and no coat.
"I won't be outdoors for long," he says kindly.
"On the bus," I say because, whenever I sit on the 176, my toes freeze.
"I'll be fine," he says.
For a moment he is tempted, perhaps, to pat me on the head.
Sometimes I think it might be easier all round if I bought a jar of Horlicks and took up knitting.
Does this ring bells with you?