What is the best way to set up a child's Xbox account to allow time limits and for him to...

Forgive me if this has been answered, I was unable to find a satisfactory answer after much time spent researching the topic...

About a year ago, my son got an Xbox. I think it is an Xbox One S. The Xbox is totally his and he uses his own money to buy games, game skins, subscriptions, etc. I do not game on it all. My son does not have an email address so I used my email address to get him going on it. I am now wanting to set up time limits for him to play. Apparently I can only set up time limits on a child account, not my own account. However, it appears that he will lose progress on his games if I set him up on a separate account which, understandably, he is not happy about. That being said, what is the best way to set up the account so that:

• I can set time limits on gameplay
  
• I have to authorize purchases
  
• I can restrict the content rating of games he plays
  
• He can take all of his progress with him some day when becomes an adult
  

Thanks for your help.

:)