Figuring out how old to leave your child alone, or let them walk to school by themselves is really a case by case basis. And I think if you look into the details of most of these laws, they do reflex that kids can be left alone for longer & longer periods of time as they get older.
The web-site I linked to is talking out when it's OK to leave kids home alone after school. And around 12 seems to be the norm in my area. Most of the after school daycare programs stop at the end of 6th grade. The assumption being that most 7th graders (youngest ~11 3/4 yrs) can safely stay at home after school for a few hours.
I know 16 year old teenagers I wouldn't leave at home alone for even a few minutes, but 10 year old who cold be left along for hours.
Mana I'm not sure about what state your in but when I was looking I saw no state that makes it illegal to leave a 16 year old overnight. (14-15 seems a more normal cutoff) But that doesn't mean you don't have local rules. I could imagine leaving my 15 year old one night but not much longer.
