Where can I find documentation on the age limit for free student accounts? (The teacher is also using the free canvas version.)
To the best of my knowledge there is no minimum (or maximum) age for people to use Free for Teachers in any role. That being said, access to Free for Teacher is given via email so depending on the policies of the email service provider there may be an effective age limitation that would affect people using that service being able to then access Canvas.
Interesting question. I'll just leave this here... https://duckduckgo.com/?q=coppa+site%3A.gov
Nice use of duckduckgo. Adam Williams turned me on to that engine.
If you find privacy law interesting or need to understand it for your work, one important concept to start with (not assuming you are at a starting point but for conversation) is Data Controller vs. Data Processor. Strange as it might sound, I am very interesting in this topic in general and would very happy to chat with you in another forum.
Retrieving data ...