What i meant is that i still have the access to my old wallet address that i mainly use at 2014 - 2016, which yes, i still do have the private key
It is good when you have access to that private key.
but unfortunately in the past i've never ever did a signed message using that address.
You don't need to have a sign message in 2014, example. What you need is have a post, or few posts with that address in 2014 or any year before the hack. Post contains that address need to be original, no edits. It is a plus point if some members quoted it for you in the past. If you pay your attention, you see many people quoted the sign message posts in the topic for Sign message.
Hackers can edit, delete past posts but they can not send request to other members to delete all past quoted posts relate to the hacked account.
Now, you sign a message with that address to prove that you are the person that owned that private key in 2014 to before the hack.
And yes I'm still new to this signed message thing, and i got a question, does signing a message with said address need the private key?
True so. You need to have private key to sign a message.