I live by nearly the same rules. No more than 3 years max, and a check in my pocket from my credit union. But I not afraid to go older if the vehicle is on hood shape and reasonably low mileage. Vehicles depreciate for age, condition, and mileage. I will take the savings of a 5-7 year vehicle if the condition and mileage are great. But they are hard to find, it often takes a couple months of looking.