You’ll need to remove your email address from your own account before you can associate it with another account. It’s a multi-step process.
1. Get a throwaway email address from gmail (or anywhere).
2. Log into your personal account.
3. Send invitation to the new email address.
4. Log out completely from all Google properties.
5. Click on the link in the email (the new address)
6. Select “I already have an account” and continue.
7. This adds the new address to your account.
8. Log out
9. Log back in with the old address.
10. Confirm the addition and promote new user to admin
11. Log out completely.
12. Log in with the new address.
13. Remove your old address from the account
14. Log out completely
15. Proceed to accept invitation to the new account. (Select “I already have an account”)