I wanted to change the age of my son but failed, how to change details of members already having in Family sharing

In Family Sharing my son age is wrongly given as 8 , which intends to be 18 , after setting up later I tried many times to change and even remove him so the wrong information will not be there but I tried my best and after I set up his Apple ID he later changed it and I was unable to do anything as the systems resist any alteration. Then I blocked all sharing but that blocked my iPhone and I again reinstated those useless information. Even this time I failed to do any changes in his identity as he doesn’t share any facilities that I can provide. Now I have asked him what Apple ID he used he refused as he thinks I can go through his information. So situations is beyond my control and I don’t want to interfere in his actions.