I suspect that even with the limited post cap the mods are reacting to player reports rather than reading every single post. So even if it was 9 months ago, if it was reported yesterday and a mod investigated and found it to be a violation of the forum guidlines/rules, then an old post could indeed attract a ban even if nothing had been done in the interim.

"Everyone else is/was doing it" is never a good excuse, it simply means that no one has reported them yet and they run exactly the same risk of a ban that you did.