J.O.
As a mother of 7 I can say your son's eating habits are perfectly normal, My oldest (15) would not touch a veggie to save his life, and still doesn't he is a meat and potatoe's guy, just like his dad, My 2nd (14) would hardly eat meat and today is a vegetarian, My next two (13 &14) are a little more "normal" in thier eating habits, My 5 year old only eats cereal somedays, but has to take a bite of everything at dinner, the same for my 3 year old although the only food she has any interest in is cheese samdwiches, and last but not least my 8 month old he so far eats anything I give him with the exception of sweet potatoes, he gets that from his momma :).
Don't over stress it unless he isn't gaining weight, and your doctor becomes worried, most kids eat a lot one day and barely anything the next, their bodies let them now what they need and when to get it. Enjoy these months with your son I love that stage it is by far the funnest.