Hello Shin Shougen,
Thank you for posting your question on Microsoft Q&A forum
I understand that someone entered your parent's email into your Microsoft account and changed your age back to 13 years old and under. even though your account has passed salutary age.
Do you have access to your parent account? Or you could ask them to go to https://login.live.com/, choose I’m a parent or guardian, and sign in with the adult Microsoft account.
- On the consent page, select Yes, I agree > Family Safety to finish consent.
- Visit account.live.com/mykids.aspx with that adult account, find your name, select Edit this child’s personal info, and correct the birthdate to your real age 17.
Because you mention that your parent email that change your account date of birth, so only their account can edit your account birthdate.
Refer to this site for more info on how to change birthdate for your account:
Feel free reply back to this post if you need further assistance. I'll be happy to help.