I hate to tell you this, but I have this with my 15 year old DD, and she has always been the same! But, in my defence, my 11 year old eats pretty much anything, and they were weaned the same.
DD15 wants to eat healthily, as she is a sensible girl, and is trying to eat 5 a day, but finds it difficult. The only fruit she likes are apples, although she will eat raw carrot, sweet corn and some vegetables. She suffers from IBS, and had reflux as a baby, so I think that has affected her feelings about eating. She also doesnt like sweets or fizzy drinks, so that's a good thing!
She generally likes bland food, such as chicken, potatoes, toast, one type of cereal etc. I could write a huge list of what she won't eat! I think she has a problem with texture rather than taste.
I would say to give small portions, and compromise, give him the healthy stuff that he likes, but limit biscuits etc! Also, don't make a big fuss about food as long as he's growing ok. When he's old enough, then explain about being strong and healthy, and set a good example by eating healthy food.
I agree with watermelon about peer pressure. Do you have any friends with older children that he looks up to? They could help influence him, if he wants to be like them!
Good luck, try not to worry. :)