I can assure you that somewhere around the 6-7 year mark, it is completely normal for kids to take public transport to go to school. It is where I live, it is in Munich (always fun to end up in the school rush hour sharing the subway with all those little ones riding the train like a pro). It is simply normal for those and nothing even remotely special or weird.

I started taking the bus to school from first grade, as did most of my classmates. I'd usually meet a couple of them on the bus and we used to time to copy homework :)