You can't keep both accounts. As per the PPF rule, an individual can only open a single PPF account in his name. Close your new account stating that you have an existing account and then follow below rule for existing PPF account.

Following rule will apply for you -
If the account is opened in the name of the minor and the minor attains majority before the maturity of the account, the ex-minor will himself continue the account thereafter. He will submit a revised application form for opening the account to the Accounts Office. His signature on the application form will be attested by the guardian who opened the account of the minor or by a respectable person known to the Branch.