There is no age restriction, and it’s generally safe to use Threema at any age.
EU users who are under 16 years of age are required by law to obtain parental consent if they wish to link a phone number and/or email address with their Threema ID. (If Threema is used anonymously, no parental consent is required.)
The app’s rating in the Google Play Store is determined by the International Age Rating Coalition (IARC).
There is a price plan available for public educational institutions: Threema Education
