I believe that kids need to have opportunities to stay home alone starting around 8 years of age. Not for more than a few minutes at this age though, it's a learning process.
If kids are legally old enough to take the Red Cross Babysitting Class at age 12 and watch other peoples kids, legally, then they better have learned how to take care of themselves by them self already.
If i am going to walk to the neighbors house to chat for a moment I allow the 8 year old to stay at home but the 5 year old comes with. I have very strict rules about what she can do while she is home those few minutes. No cooking in the microwave, no phone calls answered or made except to me or hubby if she gets scared, she is not to answer the door if someone knocks, etc...good common sense stuff.
As she gets older over the next year I will start leaving her home alone for a bit more, starting with 30 minutes, see how she does with that, then increase it if she does well.
I fully expect her to be able to be home alone for an hour to 3 hours by the time she is 12. That is the goal, it may take her longer and it will take my grandson longer due to his issues.
But kids need to learn and have learning experiences to be able to do things successfully.