It does depend on the child, but I always ask myself this.
If something WERE to happen (and of course you never know what might happen) and it ends up on the 6 o'clock news, will I feel like I made the right choices?
If you left your 7-year old home alone and (God forbid) a fire happened, what would the story sound like on the news?
Woman left a 7-year old home alone and house caught on fire. Luckily everyone is okay.
OR
Woman left 14-year old home alone, the house caught fire. Thankfully everyone is okay.
To me, common sense is a general agreement with society that you are making the best choice you could. Not many people would question the fact that you left your 14-year old home alone. Many people would question leaving a 7-year old home alone, even if he/she was "mature." I don't personally think that's good sense.
For me, I could NEVER live with myself if I left my 7-year old home alone and something happened. I KNOW that 7-year olds, no matter how good or "mature" they seem, are just not equipped to handle emergencies as well as an older child. There are many kids who are very well-behaved in my class, they are the ones I can depend on to behave even if I'm not right there with them. BUT, they also still go running and crying to their mommies when they fall down and I've seen them get frustrated or angry when things don't go their way and then they seem like any other 7-year old. To be honest kids really don't start acting more mature about things until about age 12. We had a girl break her arm in front of everyone and the only kids that kept their cool and could actually help me in that emergency situation were the 12 and 13 year olds. I had 10 year olds crying that they saw it, and one was in shock at what she saw and I had to get one of the older kids to help HER out.
I'm not saying to run your life by what "everyone else" thinks by any means. I just think the 6 o'clock news is a good way of determining if you're taking an unreasonable risk. Your child's life is not worth the risk of 6 minutes down the block. I know bad things can happen anywhere at any time, but I'd be more at peace with myself if I was sure I did everything I could.