What do you mean by signing a message with an old address of mine?
You will understand that we cant just take your word for it that the account is yours. Signing a message shows that you at least controlled the account in the past. The address used should be old, because the last time you use the account was over a year ago.
If you dont know how to sign a message this might help ->
https://bitcointalk.org/index.php?topic=990345.0Edit:
Post #213 here is the oldest address I could find for the account
https://archive.is/nYoN1Taht's the address I've used on cex.io with the same username: pasteboard.co/24MzXTJ9.jpg This is screenshot of an address.