If you created a sub account when you were younger, you can now upgrade it to a master account, here is a quote from the source:
Starting today, PlayStation Network (PSN) users will gain the ability to upgrade a sub account to a master account. We’re always listening to user feedback, and this is a feature that many of you have asked for. You’ll be able to upgrade an account first through the web and later through PlayStation 4. Instructions on how to start this process through the web can be found here.
In case you aren’t familiar, sub accounts allow users under the age of 18 to access PSN while letting parents or guardians manage their online experience. A variety of PSN features can be limited through sub accounts including messages, monthly spending limits, and gameplay broadcasts. Additional information is available on our Knowledge Center, here.
If you were on a sub account and turned 18 (Happy belated birthday!), you may want to upgrade to a master account to access the full feature set of PlayStation’s online experience, including PlayStation Store. Your profile will be carried over when upgrading to a master account, along with items like your friends list and Trophies.
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