when there is a change in your wallet file the client writes it on disk again so that creation date changes to the last time you opened it.
Doh. I didn't know that, so checking the creation date isn't going to give any useful information.
Regardless, the most likely reason behind all of this by far is you creating a wallet file years ago and forgetting you did so. If you absolutely cannot remember the password, then as far as I can see you have two options available to you:
Use the link posted above by BitMaxz to attempt to brute force the password yourself
Use a reputable and trusted third party (such as Dave from Wallet Recovery Services:
https://bitcointalk.org/index.php?topic=240779.0) to attempt to brute force it for you