My son is 12 he often rides to from school 5km each way and rides to mates house 1km away. He doesn't have a mobile but we have a "spare" that we insist he takes to text us that he arrives safely each way of every ride or walk.
We leave him home as and when he chooses and we have rules that differ to suit the situation.
It's only been this year we have felt comfortable with this. He is very responsible and trustworthy however I just wasn't ready to take any risks with his safety.