>>280873318
>some girls don't even start their periods until 13 or 14, and plenty don't develop breasts (the main visual indicator that you're ready to procreate) until 14 or 15.
Anon your data is about 100 years late, only a small minority of girls are that late in development. The damage from massive uncontrolled pollution from industrialization and some starvation like events in history is almost healed in modern times.

Using data compiled in
>[Yasudajuku (Yasuda Yasuhiro, Shinchou ni Kansuru Kousatsu)] Kodomo no Hokentaiiku Children's health and physical education [English] [Weeping_Pirate] [Digital]
Then we will see that the average menstrual rate for (japanese girls) 11, 12, 13 ,14 15 is:

11 year old girl
>25.2 %
12 year old girl
>57.6 %
13 year old girl
>82.8 %
14 year old girl
>95.1 %
15 year old girl
>98.7 %

So if you for example had 100 14 year old school girls in a room and asked them how many have had their first period then about 95 would have had it.


And when it comes to the breast the the average girl at 12 have reached tanner stage 3 which is defined as "breast begins to become more elevated, and extends beyond the borders of the areola, which continues to widen but remains in contour with surrounding breast"

At 13 it is at stage 4, 14 year stage 4 and 15 it is at stage 5 which is adult size. Pic related height wise at 15 they are practically speaking almost done growing height wise.