Yep, the email they sent out is terribly worded so it looks like the age requirement is for Zed itself.
Their actual blog ( https://zed.dev/blog/terms-update ) says the age requirement is only for their AI service (still not the best wording but a little clearer):
> Age requirement. You must be 18 or older to use Zed’s AI-enabled software-as-a-service offering (the “Service").