Appetite reduction with age?

My male sheltie is 8 years old. He is approximately 27 lbs. His feeding schedule has been twice a day since I have had him about 5 years. Recently he has not rushed to the food bowl when it is time to eat. My question is: As my sheltie gets older, does his appetite naturally decrease or is this an indication that he may need more activity to increase his appetite since he is getting older?

Take him to the vet & check for a physical cause. If he's healthy, then he may not need as much. Or he could be bored with his food & want a different flavor. Or canned, if he's not getting canned.