Hello, and welcome to the forum !
The keylock was only incorporated sometime in the last 10 years or so. The PT92 has been made for a very long time, and there are many that don't have the keylock. I wouldn't worry too much about that.
If you go to the Taurus website www.taurususa.com you can find a link that will allow you to search on your gun's serial number, and it may tell you when the gun was made.