I started leaving each of mine home alone for short periods (<1hr) from age 10. I think they're capable of keeping themselves safe for an hour or so from that age.
What would worry me more about the "getting home from school and being alone for an hour" is the translation from school to home being alone. It's a pretty stark contrast from micromanaged time, noise, bustle, attention, business to a silent house all alone, and I think most kids would benefit from that time being buffered by a caregiver.
Until secondary school I used a childminder to collect from school and buffer the time until I finished work. She was able to tell me that children had come out of school quiet or upset or excited or happy, and she was there to phase school in to home.
Since my older kids started secondary I now need to collect them every day as there's no bus and they won't go to a childminder (though had geography worked out, they could have continued with the primary childminder). So I'm there to do the buffering.
Safety wise, I would say 10 years+ with some prep and close emergency support. Emotionally, I'd try and have an adult regardless of age.