Pet sit. Animal lovers should have no problem making a few extra dollars dog walking or grooming. Also consider pet sitting when owners go on vacation or travel for work.
Tour guide. History buffs should look into a post-retirement job as a guide at a local museum or historical monument. A part-time tour guide position will allow you to share your knowledge with others and interact with tourists from throughout the world.
Ask for discounts. Some senior discounts are well publicized, but others are only available to those who ask. One of the best perks of getting older is getting a discount simply because you're willing to admit your age.