I agree that it depends on the child and the situation. DS1 was first left alone for very brief periods at 8, routinely for about an hour at 9, and often for slightly longer periods at 10. DS2 felt uncomfortable alone at 8 ro 9 and so was not left alone until he was older.
It's amazing how varied this is in law, in cultures, and in practice. I was first left alone at 5. By 14, I spent a day by myself in East Berlin without knowing the language at all just figuring out things for myself. In retrospect, that seems so young to me, but I was quite independent and eager to explore.
