At least they have company, I suppose. At our primary school, in the early 70s, from a year containing almost 90 10-year-olds, only one child was clearly undergoing puberty. It set her apart, not least because she embraced it so enthusiastically. What a to-do, when we all went to the baths for swimming lessons. Little boys in children's trunks. Little girls in children's swimsuits. Gillian in a purple halter-neck bikini, looking like something out of a Bond film.

She didn't care about us, or the gulf of consternation and discomfort that had isolated her from her classmates. She was already gone, the social life she shared with "older guys who have cars" so incomprehensible that it wasn't even disapproved of. At secondary school, she just drifted out of view, afloat on her notorious breasts, each, distractingly, far bigger than her head.

An authoritative Danish study has found that girls, on average, now start breast development at the age of nine years and 10 months, a year earlier than in 1991. No one knows what is driving the age of puberty down – maybe it is just the consequence of better nutrition, or maybe there is something in the water. Research continues.

Whatever the reason, the phenomenon is worrying, to say the least. In a complex and recklessly sexually liberal developed world, the time needed to prepare for adulthood, emotionally and intellectually, is surely much greater than ever. Instead, childhood is becoming briefer, and minors with the bodies and the desires of men and women are more common. It's a profoundly sad modern paradox.