Well I have gone through this 3 times in my life, and each child is very different.
My take on this with three grown sons now.....
I would not leave a child home alone unless they are 16.
I would not leave a child alone when 16, for more than 4-5 hours.During the day.Forget night time.
It sounds crazy, but guess what they can 'get-up-too''? while your away.!!
Girlfriends come over, the next thing is, well need I say more.
If you have a girl, then boyfriends come over...No use saying you don't want them to do it, they will anyway.