The person that is selling it has a fleet of 50 trucks that pull dry van (fedex). From the little I know and the maintenance info he provided, seems like they do a decent job at keep up their trucks.
It's idles about 50% of the time based on the miles and hours you noted. Still if it is maintained that makes a big difference to any engine.
When I drove for Sun Coast Resources, I was issued a straight truck that had 150,000 mi, with over 30,000 hrs. The truck started life assigned to ‘frac fueling’, then moved to local delivery as ‘hot fueling’ frac’s was dieing out. I pulled a 5,000 gal pup behind it, dang that was a nice truck, long-nosed Pete daycab, 18sp transmission, huge Cummins engine. Unfortunately, it had a single channel frame, developed a crack, and the company would not repair.