Apparently some accounts can have their edit window muzzled if a moderator chooses to. I have a reduced 10 minute edit window that was applied to my account without notice or explanation, it's fully possible that you might have one too.
Huh. My other comments are editable way out.
I think mine is like 30 minutes.
How do you know what your edit window is?
I refresh the page until the edit button isn't on my comment anymore.