Girls start earlier and finish earlier. Boys start later and keep going. The endocrine account of this is well established, and worth setting out first. What Korean Traditional Medicine adds is an interpretation of why two schedules might exist at all — and a fish experiment that makes the underlying point rather neatly. This article covers growth timing in boys and girls.
In Summary
- Girls enter puberty roughly one to two years earlier — typically ages 9–10, with peak height velocity around 12. Boys start at 10–11, with PHV around 14.
- Oestrogen drives rapid early growth but also accelerates bone maturation, closing growth plates sooner. Height growth largely stops within about two years of menarche.
- Testosterone acts more strongly in later puberty, so growth accelerates gradually and the growing period runs longer.
- Growth plates typically close at 16–17 in girls, 18–20 in boys.
- During PHV, girls gain roughly 8–9 cm a year; boys roughly 10–11 cm.
- So girls are taller earlier and boys finish taller.
- In my interpretive framing — not as an established doctrine — the traditional yin-yang reading offers a why: building a large frame is metabolically expensive, and a body that must reserve capacity for pregnancy has reason not to spend everything on size.
- A fish experiment illustrates the trade-off: faster growth, shorter life.
- What can shift the timing earlier: sugar intake, stress, reduced activity, and dopamine-driven screen use.
The Endocrine Account
Look up why boys and girls grow differently and you get hormones and secondary sexual characteristics. The difference comes down to three things: when puberty starts, how the sex hormones act, and when the growth plates close.
When puberty starts
Girls generally begin about one to two years earlier — on average around ages 9 to 10, reaching peak height velocity (PHV) at about 12. Boys begin at 10 to 11 and reach PHV at about 14.
How the hormones act
Oestrogen produces rapid growth in early puberty, but it simultaneously promotes bone maturation and closes the growth plates faster. This is why height growth largely stops within roughly two years of menarche.
Testosterone acts more strongly in the later phase of puberty. Growth accelerates gradually and the growing period is sustained for longer — the main reason boys finish taller.
When the plates close
Girls’ growth plates typically close at 16 to 17. Boys’ remain open until 18 to 20, giving a longer window in which height can be added.
And the rate differs during the peak: girls gain about 8 to 9 cm a year during PHV, boys about 10 to 11 cm.
So the picture resolves: girls start earlier and are taller first; boys start later, close later, and grow faster at the peak, finishing taller.
A Reading of Why Two Schedules Exist
What follows is interpretation, and I want to mark it as such clearly.
This is a reading about physiological function as it settled tens of thousands of years ago. It is not a claim about social roles, and I hold no view that men and women ought to occupy particular positions in society — I run a household and share the childcare myself. Read what follows as an account of bodies, not of how anyone should live.
In the traditional framing, yin (음 陰) gathers energy inward, condenses it, and is suited to producing something new. Yang (양 陽) disperses energy outward and is suited to bringing things in from outside.
For a species to adapt in a natural environment, there was use for both: individuals who could raise young well without needing to be large, and individuals whose size served contest with the outside world for food. Pregnancy and childbirth demand a great deal of energy and are central to the continuation of the species — so spending heavily on building frame size is not advantageous for a body that must reserve capacity for that.
Whether one finds this persuasive, it produces a testable-sounding proposition: growth and longevity trade against one another. There is an experiment that speaks to it.
The Fish
Morgan Housel’s Same as Ever recounts a study in which young fish were raised in cold water and warm water respectively.
The fish raised in cold water grew more slowly but lived about 30 percent longer than average. The fish raised in warm water grew quickly and died about 15 percent earlier than average.
The proposed explanation is that rapid growth causes tissue damage, while slower growth allows more resources to be allocated to maintenance and repair.
Hold that alongside the growth plate picture and something useful appears. Early, fast development is not straightforwardly a good outcome. It shortens the window.
What Warms the Water for a Child
Being overweight is understood to bring menarche earlier. In the terms of the experiment, something is acting as warm water. What, in a modern child’s life, generates that heat?
- Sugar intake. The basic nature of sugars, in KTM terms, is fire (화 火).
- Stress, and the appetite that stress drives up.
- Reduced activity. Heat accumulated in a child’s body needs running around to disperse it.
- Dopamine stimulation. Video watching and gaming to the point of compulsion generate heat in the body.
The body a child is born with is much the same as it was tens of thousands of years ago. Where there has been an abrupt change with no precedent, the environment is the place to look — and the adjustments follow from that.
They are not easy pieces of advice to act on. I am aware that “reduce screen time and let them run around” describes a household most parents are already trying to run.
A Note on Scope
None of this is a method for controlling when a child enters puberty, and it should not be read as one. Early secondary sexual characteristics — breast development before 8 in girls, or testicular enlargement before 9 in boys — is a matter for paediatric endocrine assessment, not for household management. What is described above is ordinary healthy living, which happens to run in the same direction.
Summary
Two schedules, two hormone profiles, two closing dates. The endocrinology explains the mechanism; the older framing offers a guess at the reason.
And the fish are worth remembering. Growing fast is not the same as growing well.
Related: Does Weight Turn Into Height?
