It's not abnormal for them to go through hunger strikes. I have heard that the record for a ball python not eating is somewhere around 23 months!!!

As long as he isn't losing weight, and everything is good in his tank (temp, humidity, etc), then I wouldn't worry about it. Just watch his weight, and offer food every now and then. He will eat eventually.

Have you changed anything in his home lately? Like a new hide, or new plants or anything? Sometimes the smallest change in their surroundings can really add stress to a snake, thus causing a fasting period.