I was 10 when I started. I had no idea what was happening when I arrived at school one morning, saw blood in my knickers, and ran all the way home in tears. My mum calmly said "Oh, you've started, have you, hang on a minute" and she passed me a belt and pad! I had to ask what it was.
My younger DD started at age 9.5. I had already talked to my girls about periods, so she wasn't upset about it. She went to a small primary school with outside toilets and no sign of a sanitary towel machine, so always had to be prepared. I couple of years later I was on the PTA when we were discussing improvements to the school building, including new indoor toilets. I made the point that they should include sanitary product machines, but the chair (a woman) immediately laughed and said "Crikey Meg, this is a PRIMARY SCHOOL. I'm the mother of four girls and believe me they don't start their periods while at primary school".