I was going through the demo and perhaps I missed it. But this is also a problem with the current blogging software I use from a different development. And before I migrate to Woltlab I really need this feature.
I would like to set a maximum edit time for blog post and blog comments. I find when someone has an unlimited edit time, it is easily abused. It's not good if today their blog is about "X" and 3 months from now they edit their blog to add spam. Just as it is no good if they have 1,000 blog post and later decide to go on a mass delete spree.
So if this is not a feature, I would like to suggest it (if it is and I've overlooked it, please let me know). This would be far to important to depend on an addon (if there is one).