look in Board configuration> Post Settings> Limit editing time: Limits the time available to edit a new post. Setting the value to 0 disables this behaviour. setting this to "0" should allow endless edits.
I'm having that same problem.. Users are unable to edit their posts. There is no edit button. Admins also can not edit. Delete and report are available. Limit editing time is set to 0 as notesd above.
if you give endless editing time you may loose moderation control over your forum .... if a person edited to add prohibited material on post after editing 1month old post , how do you know ? so there is no use of moderation here