Google Wallet's fingerprint support has finally gone live as part of a small update to the application. In addition to Fingerprint support the app has now changed to using the Google Account PIN instead of the payments PIN like before, though you aren't required to use this unless you want to use the fingerprint to unlock the application. If you do want to use your fingerprint, you'll be greeted by the changes once you open the app up, and you'll be given the option to switch to your Google Account PIN, but keep in mind that you may want to figure out what it is before you switch as you'll be asked to enter it immediately after accepting the change, and if you don't remember it the whole process just becomes a tiny hassle.
After this step you'll be able to accept yes on using your fingerprint for all future unlocks, though you won't need to unlock with your fingerprint every single time you go into the application as it stays unlocked for a period of time. That being said you can always manually lock the app anytime you want from the hamburger menu. Simply slide open the menu and direct your gaze to the very bottom where the option to "lock now" is located.
It is worth noting that if you choose not to switch to your Google Account PIN, the only other option is to not use a PIN anymore at all which would leave your Google Wallet app unsecured, so naturally transitioning to the new PIN use is recommended. From inside the settings menu there's an option to change the Google Account PIN if you want to and you can also disable the toggle from the same place if you end up deciding you don't to use a PIN with Google Wallet after all. In this part of the Wallet settings menu there is also a toggle for disabling the fingerprint sensor for the unlock method, and the option to set your default lock time, so if you want it to lock quicker or have it stay open longer then you can do so, but there are only two options here which include a 15-minute auto-lock or a 1-day auto-lock. If you haven't seen the fingerprint support yet it should be showing up soon.