My daughter is 11..I have left her alone for up to an hour and only during the daytime, never at night. As for leaving her home alone for a full day, not sure. I havent really thought about it...maybe 14 years old depending on how responsible she is.
My son, who is 2 years old, has a loooonnggg way to go before he will be left home alone.
I dont remember when I started being left at home alone...middle school or early high school. It wasnt that of a big deal to me which is probably why I dont remember.