OIL - Change or not to Change

I am more to change oil, according to mileage instead of time.
I know the oil has been in my Duster for over 4 years on a fresh re-build, but it has no miles on it, less than 100.
I still looks clean.
Daily drivers get changed with mileage also.
I changed my old 03 jeep wrangler over to synthetic when it 20K miles on it, I would spin the filter off every 5K and change it every 10K. It is still going strong.
My dad does the same thing, his old 78 power wagon he bought new, he changed to Mobil one on the first oil change. At 213K the rear main was leaking so bad it smoked the clutch.
Pulled the engine to fix the leak, dad said rebuild it, I pulled a few bottom end caps off, no wear. Re-gasket it, put in a new oil pump and timing chain, it still had cross hatches in the cylinders, un-heard of for a high mileage LA 360.
The old engine still runs fine to this day, but the truck around it is wore out.