You still have about 40% life left in those old pads. You can run them down to 1/32 if you like, just make sure you don't let the friction material completely go away, or you'll be metal on metal and you're rotors will be destroyed.
Good rule of thumb is about 2/32 or around 2mm, too keep it safe.
Here in PA for state inspection 2/32 is the state minimum, below and it fails.
Our factory wheels are so easy to look inside of that as long as you monitor them you can run them down safely and get all your money's worth.
Edit: spelling, too early lol.