I'm in no position to assess this paper as it's archaeological but there are some interesting distinctions between the age of entering puberty, the age when menarche happens, and the age at which puberty ends.
Puberty is divided into five clinical stages, with pre-puberty at stage one and onset (or thelarche) at stage two. Menarche (a girls first period) occurs at stage three. The age at which a child enters puberty (stage one) varies. Today, puberty onset occurs between the ages of ten and 14 in girls and 12 to 16 in boys, with some ethnic groups starting around a year earlier. The end of puberty, or full maturation, is reached by 13-17 years for girls, and 15-18 years for boys.
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A girl’s first period is a significant milestone in her development, but it is a highly variable and environmentally fragile indicator of maturation. Today, menarche starts at a median age of 12.5 years in the UK, with 2-3% of girls experiencing menarche at ten.
In England, just before the industrial revolution, historical sources suggest menarche occurred between 12-14 years. By the 1840s, girls had their first period between 14-17 years. While we have a rich record for ages of menarche, there are no written sources to tell us when children in the past first entered puberty.
We're introduced to a fascinating study about bones in medieval England and using bone markers to assess the stages of puberty.
The average age at which children entered puberty was the same as for most boys and girls today: between ten to 12 years. But medieval teenagers took longer to reach the later milestones, including menarche.
The adolescent growth spurt that signals the most obvious external physical changes occurred between 11-16 years, and menarche at 12-16 years, with the average age at 15 years. In medieval London, some girls were as old as 17 before they had a period. And boys and girls did not complete their adolescent growth spurt until 17 or 18 years.
For these teenagers, growing up in a rapidly expanding and overcrowded London, 26% had not completed puberty before they died at 25 years of age. The age at which modern and medieval children progressed through the pubertal stages after puberty onset was different.
research.reading.ac.uk/research-blog/children-arent-starting-puberty-younger-medieval-skeletons-reveal/