The puberty process starts internally around 8 years old for both boys and girls.
The “GnRH” starts dripping or spurting like a clock at regular intervals and starts making internal changes.
It takes a few years for effects to show up (mustache and stuff).
Meanwhile, a lot of internal stuff is happening.
So by 9 years old, thoughts are stirring and stuff already. If it happening too quickly or causes emotional problems, there’s temporary puberty blocks for precocious puberty but it might just be a case of a “time for a few talks” and some education materials maybe, I dunno.