At only 2 to 3k miles a year I'd go two years for the oci. My '99 Ford pickup gets new oil every other year and have been doing this on it for 10 or 11 years now. I do put a little more miles on it than your son does but I still don't get over 9k miles for the two years. Heck I have to change out my tires due to age(rot) well before they run out of tread.
ROD