Obviously that's not an ideal situation for a child, but it's pretty common to have children from the upper-grades walk home to an empty house alone while their parents work, at least around here.
Truancy is another question. Without a proper homeschooling plan and progress towards it, the nine-year-old could not stay home alone during the school day.
But the point is not so much one age--it might differ by culture, state, country, whatever.
The point is that there are legal obligations I have towards my kids, and I'm not going to get caught neglecting them.
I don't say this to make them feel unloved. I try to buffer it with statements about how we're a family and we love and want them BUT supposing they don't accept that, well, it's not really an option, either.
