I am 25M and have that same dull aching LUQ under the rib fullness type of pain now for 6 months. It appears from the previous discussions (over >10 years worth) that there could be no anatomic abnormality. The only concern for you is age, and I agree with Kaneda2112 that you should get it checked out just to be on the safe side.
Is there any correlation to diet and the occurrence of this problem? Any trigger foods?
Apparently, left side abdominal pain is often more common in women and young adults.
There are lots of common causes of a left sided abdominal pain, enlarged spleen, bowel problems, like diverticulitis, and constipation, to pain arising from muscles and skin over the left side of the abdomen.
I have a friend who has chronic pancreatitis with similar symptoms. You should get this checked out if it's interfering with your everyday life.
What testing have you had done? What have you tried as far as meds or other?