Yep, that area is problematic and you can find related discussions in this Discourse.
Please first read the following (item 1):
https://commonvoice.mozilla.org/en/terms
AFAIK, that clause came a bit later into the project, probably with changes in EU laws, so age 19 became an edge case. For legal reasons in many jurisdictions, one might not use recordings from minors during model creation. But “minor age” changes from place to place and in time.