We had a lot of trouble getting Flynn to eat in his high chair. What we are doing at the moment (which is still working after a week or 2!!!) is having him sit on a booster seat at the table with us. I agree with the big boy statement. I think that was Flynn's beef! He has a spoon and holds it in one hand while shoveling food with the other. It is quite messy but we have a plastic drop cloth underneath him and a towel on the table for easier clean up!
It may aslo be that he just has a small appetite. Try not to worry too much, if he is happy and active and learning new things etc I wouldn't be too worried. If he seems sickly and is not progressing/developing well then be worried.
Hope this helped