Last I heard it was 5 minutes to edit without edit tags showing up, but you could edit older posts going back quite a while (albeit with the edit tag showing when you edited it). But recently, Demiurge and Federal Farmer seemed to think there was a conspiracy to edit old posts to make them look crazy, so I think something got changed.
You can edit 5 minutes before the post shows as edited. You can edit your post up to 30 minutes later, at which point you can no longer edit.
Do not like. To this day I can go back and see typos in posts I made years ago and be annoyed by them. I used to fix those when I saw them.
People lose the ability to edit posts if they're found to be abusing the edit button. As of this post, only 1 person has been prohibited from editing their posts.
Wasn't it Dayton? I think it's probably time to give him back the ability to edit posts. He hasn't abused that in a while.