If you are registered as under 16 years old when you first start playing or register a login account on either the Nintendo Switch or mobile version, you will not have access to the chat feature or other age restricted features even after turning 16.
After turning 16, you will need to link a Pokémon Trainer Club account to adjust the parental controls for your Pokémon UNITE save data.
*Age restrictions may vary depending on your region of residence.
Enter your Pokémon Trainer Club account login details by accessing the following location:
Settings > Account Settings > Pokémon Trainer Club