Id be much more suspicious that it is due to childhood obesity. I had an earlier period then many of my friends because I was a heavy child despite my parents efforts. One of my friends who was always slim to underweight was the slowest to have a period(late teens)
For example I keep horses and in order to get a heifer calf ready for breeding seasons we need them to hit certain weight gains at different ages. if they don’t hit those weights their heats are often delayed.if they do hit targets they are often ready to be bred quite young. Weight seems to be massively influential to them.
Humans are still biologically… just another animal.
My hypothesis is that being heavier consistently throughout childhood and as a result their bodies are reaching biologically adult weights sooner leading to early periods etc.
Drinking milk id imagine is incidental.would be interesting to check it against other nations where childhood obesity is an issue but dairy is uncommon if possible.
In the eu hormone use is much more tightly regulated then in the us or Australia and each drugs has the withdrawal worked out and thats strictly enforced. We dont have a lot of antibiotic and hormone contamination at all as its a very strictly regulated industry.