Ok so my experience is from my teenage days, so take it with a grain of salt. I started shaving at that age because I had arm pit hair, and I think I started shaving my legs a year later? My mom was very clear in that I had to be very careful, not do it too often (sensitive skin), and tell her if I cut myself. It made me feel a lot better and less self conscious. Hope that helps!!
I let my 9 year old shave. She grows thick hair and she’s a gymnast so she feels more comfortable at meets if her legs are shaved. She’s super responsible and grown for her age though