The main indicator for age or wear of a DSLR has been the shutter counter, hidden in the metadata of an image file.
This will most likely change in future. With the D850, Nikon implemented a “silent mode” for the first time, which utilizes an electronic shutter in live view mode. A picture is taken without any movement of the physical shutter.
Unfortunately the hidden counter in the EXIF data is inremented for every exposure, even when the physical shutter did not move. This is rather strange, as it was before identical to every open/close cycle of the shutter. Activating live view without taking a picture increments the counter also.
The addition of silent mode turns this counter now into a simple total images taken indicator, no matter how they were taken.