I work for an GI doc and you would probably have more symptoms then this. I do though recommed finding a good GI doctor in your area and let them know of your Family History. They may want to do a Colonoscopy and its not bad the worst part of everything is the sitting in the bathroom the day before. SO relax but be aware. Good Luck! :)
at your age, it's unlikely to be anything as serious as cancer. the previous poster is correct: it could be some sort of inflammatory bowel issue. could also be an absorbption issue with your liver. let your doctor sort it out.
It's probably not cancer -- other gastrointestinal issues could be the problem here like IBS, crohns, celiac, etc etc... which can cause greasy stool, but obviously the only way to know for sure is to call your DR.