Here's the car seat manual link. Right on the first page after forward facing it says the typical data and at least 2 years old.
https://www.coscokids.com/amfilerating/file/download/file_id/5980/ Basically it's illegal to use this seat forward facing before 2 because that is what the manufacturer says is the requirement. A lot of states have a clause stating you must follow the guidelines in the car seat manual instead of doing age or weight laws. It was a bold move cosco did when redesigning this seat.
You still need to follow the rules of the seat on the plane. If you're using an infant bucket, they aren't able to force you to forward face it. If you're child is 20lbs and the seat says 22 to forward face, you can't forward face. Well you could, but it goes against the manufacturer guidelines. Sure, there are no police that are going to jump out and arrest you, but I am a fan of following the car seat guidelines. Plus, if it's a seat you have a to manually change the harness then it saves you from bothering with that.