Lets hold on for a second with destroying old questions. Doing anything in mass always has me a bit concerned.
What I'd like to propose instead is do the following:
All questions still open with those releases be closed as off-topic with a similar comment of:
This release of Ubuntu is no longer supported and is now End Of Life (EOL).
With links to supporting documentation.
That was the easy part. I'm conflicted as to what we should do with old questions that are already answered. Honestly we should first find the version specific questions with extremely high views and amend the top of the question with a post notice about upgrading and that these are now EOL. But I think, for the most part, old questions with these versions that don't get a lot of views and are already answered are just Okay. Going commando on them is only going to disrupt the current moderation process for users as no one really be focusing on the current queues and just waste votes and hunting for these demonized low hanging fruit. As they pop up (get bumped with new answers and the such) we should just close them then.
I would also like to point out that not EVERY SINGLE QUESTION MARKED WITH THAT VERSION ACTUALLY PERTAINS TO THAT VERSION AND EACH SHOULD BE SCRUTINIZED BEFORE BLINDLY PASSING JUDGEMENT. A decent amount of these can just be updated or have the version removed and still be relevant to today's releases.
I'll try to bake a data query later tonight to help identify potential questions.