Exactly what "things" did your son mention?
It seems to be human nature for people to try to find something to demonstrate their knowledge, especialy young adults to their parents. They're subcosciously stll struggling for respect as an adult.
I recently dealt with this myself. I helped a close friend find a new used car. After searching for a very long time (2 years about), looking at countless cars she found a 2002 Corolla with 58,000 miles on it in truely like-new condition. She showed it to both her grown girls and their husbands. They all found reasons to question it.
I test drove the bejesus out of that car and then went through it with a fine tooth comb. Every bolt. That car is truely in like-new condition. The normal wear patterns on the bottom door jams, the plastic scuff protectors, the kickpanels, the pedals, and the carpets aren't even there. Since she bought it, I've driven it for day trips (with her) a number of times. It's in perfect condition.
If your car is running great and you've seen no signs of abnormal wear, than without additionals detail of your son's comments I'm inclined to think your son is simply acting like a normal young adult. I would not lose any sleep over it. It is not unhealthy.