Unable to create profile for certain apps because of age restrictions

i am trying to create a profile for my son for the app Homey which is a chores and allowance app. We have an established family sharing account & everybody has their own Apple IDs (for multiple years ) with their correct date of birth listed. My daughter whom is younger than my son can use her Apple ID to make an account for this specific app but my son cannot. I will list the error message it shows. If it was just this one app I wouldn’t care as much but this is an on going issue. Plus with it being an app for children you would think it would let him create a profile. I have parental controls set up like using screen time I have went through and made sure my sons mirrored my daughters as she is able to make an account. And I still wasn’t able to make an account. I have accounted Apple via chat and they weren’t much help :( any thoughts???