Whats the legal age a child can be left alone?
Its not the age that matters so much, as long as you trust said child to be alone and you can tell they are comfortable with it and you know they will be safe then its ok. So, you couldnt leave them in a cold house with no food for two weeks, but if you leave them for the day and you leave them a couple of ready-prepared meals and check that they are okay with being left then its pretty much ok.