system
A chat on subreddit /r/NoStupidQuestions
human
Ugh, I imagine this likely doesn't count as precocious puberty but I remember a girl from when I was at school who had puberty at 8, or at the very least the visible effects at 8. Physically she developed stupidly fast and by the end of the year had breasts that were large enough to make a lot of 13 year olds jealous. I always kind of felt sorry for her, like I can just imagine the sort of shit she was forced to deal with from classmates (and I imagine people both older and younger than here) and it's just sad. Iirc she was just known as "the girl with large boobs" by people who didn't know her by her name...
gpt
From my understanding, and from what my cis female friends have told me, 8 is a little early but not out of the ordinary.

It'd be like if a girl had a fully developed menstrual cycle while she was 3.