I think it depends on the child, the dog and the area you walk - I was volunteering for the RSPCA at 13, and walked the occasional dog (it only had two temporary kennels) alone in the local area - I know that they don't let children that young do it now, though
I *might* let lil'bit walk a single, steady dog alone when she is 13 if I am confident in her ability to handle the dog
Fortunately we don't have to worry about theft here; but handling a dog-on-dog incident is a different matter
She is doing incredibly well with her confidence and handling - and fully intends to drag her parents to YKC Camp as soon as she is old enough
, so I will probably have more confidence in her than I do in some adult handlers I meet long before she is 13
Perhaps he should "prove" to you over the summer that he is responsible enough by taking control of him while you are out together - if you are happy, then you can begin to relax the rules