Click on this link to learn what it means if an app asks to track your activity --> If an app asks to track your activity - Apple Support
"In some circumstances, the "Allow Apps to Request to Track" setting can't be turned on, including:
For users with child accounts or under age 18 by birth year, signed in with their Apple ID."*
Make sure you have the correct birthday set. If you recently turned 18, try logging out of your account and back in again as worked for multiple users in this topic --> App Tracking Age Requirements Issue - Apple Community
Click on the link to read how to 'Update the birth date associated with your Apple ID' - Update the birth date associated with your Apple ID - Apple Support
*I wonder about that "by birth year" bit. If it is going by year alone it may think you are still under 18.
If you wish to ask Apple about this:
Choose your country or region - Official Apple Support
If you need to speak with Apple about this, refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This page has telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support
