@sozobe,
agree with soz.. including 'absent other issues'.
I was at my most shy and vulnerable at twelve, really unaware of trouble possibly at my door (even though I watched various stuff on tv and stayed up late, it didn't have to do with me, I was just learning). But even I was taking two buses from school, the second one alone, before I turned thirteen.
My bro in law taught my niece how to make it across LA by bus early (Mar Vista to Burbank), maybe when she was thirteen and maybe earlier, twelve or eleven, I now forget. I remember being shocked, but it was a part of a pattern, and also necessary some of the time, as the mother had shared custody, and dad was at work. (Niece told me later her mother sent her to friends' to take care of her, and not just for a day, spent the child care money on...) He taught her how to bicycle everywhere, how to camp out despite her distaste, and so on. She has grown up into a woman who can make her way in a lot of places with confidence and still be psychologically sensitive to others. I had something to do with that, but not anything to do with making her so self sufficient.
But looking back, buses across LA at eleven? Still, far as we have talked about, and we've long talked straight when we get to talk, the trauma was at the other end.