Wow, and I thought I didn't drive much.
My 2017 6 is 3 years and 3 months old with just over 10,000 miles on it.
I also have a 2002 Pathfinder that I drive sparingly now. Maybe 2000 miles a year, if that much.
I change the oil once a year in the Pathfinder, and I've done 3 oil changes in the Mazda, in a two and a half year period.
I'm thinking in your case, somewhat depending on what kind of climate you live in, that I'd go once a year, and go with synthetic.
Synthetic oil probably has no advantage unless wild is in frigid cold winters or blazing hot summers.
What matters most is the type of drives. If he drives daily a couple of blocks where the engine oil never gets fully warmed, that's tough on the oil. I'd change every 6 months. If he drives once a month for 175 miles, I'd change the oil every 2 years. Oil deteriorates very slowly when it just sits in an engine.