Reading Lessons on own

At what age did you all let your kids read their own school books without you?  I have a 7yr. old who is a very fluent reader and started reading at 3 so he has had much practice on his own.  I know CM said we should let the kids read and eventually get to a place that they should be able to do all of their reading on their own but when?  Should it be by age or ability?  What if the narrations aren’t as good as you like after they start reading on their own?  I do plan on making some subjects required reading with me but what should he do on his own and when?  Thanks for any advice…don’t want to push but don’t want to hold back.  🙂