Read the forum guidelines
How do I delete an older post here? All I can see is the option to edit an older post
I don't think you can. Why would you want to?
Only because it's no longer needed but I guess your right that we can't delete them.
It's a good idea to keep questions because someone else may search google and come across them. It helps answer questions before they are even asked. They are locked after 1 month of inactivity though.
Your right
As long as nobody replies directly to your previous post, you can delete it. If someone does reply, it's locked in; however, you can edit the replied-to post.