Diego, you are correct.
I’ve got a number of topics posted. I went to my most recent… and there’s a pencil icon to edit it. However, if I go back over a month to an older topic? That pencil is no longer there, and it’s not hidden in the ellipse expander either.
So it seems that there’s a forum default setting for the editable timeframe of a topic. I wonder if that can be set to infinity? Or, perhaps something like 6 or 12 months, and then if someone needs to correct it, contact the admin to release it for editing?