I'm sitting at 82k on a june 08 car. The battery is definitely aging. It doesnt have issues starting the car - the motor catches as quickly as it did 4 years ago. But the battery has issues motivating my top now. It struggles with it, when the car was new the top went up and down on battery as quickly as it did on the motor.
So ive effectively lost that functionality, but its nothing major. I still expect the battery to start the car for another couple of years.