I've only recently started letting my 12yo DS stay home alone for any length of time. Usually no need for more than half an hour, and so far probably an hour max. He his own key as of a few weeks ago so that he can go home straight from the school bus instead of coming to meet me at work.
This week I've made an appointment after work, which means he'll be home alone for about two hours, then need to lock up and walk up to his dads when he gets home.
He's my only DC and I never ever came home to an empty house all through high school, so probably being a bit OTT, but does 2 hours home alone seem reasonable?