If she could "steal" your phone and change the age on your account then it means you had multiple levels of the security on your account compromised and really need to make sure only you know things such as passcodes and passwords. That and take better physical security of your equipment although getting access to account settings can be done from anyplace with a web browser and security information.
Read this document if you think your Apple ID has been compromised. --> If you think your Apple Account has been compromised - Apple Support
For iOS 15 or earlier, if you want to see if anyone else has access to your device or accounts, click here --> Limit access to your iPhone or iPad - Apple Support
For iOS 16 or later see how Safety Check on iPhone works to keep you safe. How Safety Check on iPhone works to keep you safe - Apple Support
Use the information in this document to check your Apple ID device list to find where you're signed in --> Check your Apple Account device list to find where you’re signed in - Apple Support
Related materials:
Personal Safety User Guide
Personal Safety User Guide - Apple Support
> open the Table of Contents and review the articles
A document with general information about security and your Apple ID --> Security and your Apple Account - Apple Support
Contact Apple for help with Apple ID account security. This page provides country-specific Apple Support contact information ➞ Contact Apple for support and service - Apple Support
