I'm running on v.18.104.22.168
I've tried making new projects, comps, restarting AE, and nothing seems to work. The Template checkbox still won't show up.
You don't need it. Just import the AE file into Premiere and choose the sequence you created.
Davide is correct. We've improved Live Text Templates in this release, and the checkbox is no longer necessary -- editable text is enabled by default. You can also save live text templates as a single file now (including their assets!): right-click on the comp in the project window and choose "Save as Text Template".