Here is a great long list of restaurants, grocery, and retail stores, etc. that offer discounts, sometimes substantial discounts, for seniors. Check the age, day, or days the discount applies. It is always best to ask at each individual establishment.
A lot of the places don't have this information posted, so you should ask at each place that you shop at, since there can be other places too that aren't on this list. This list is quite accurate, to the best of my knowledge, but at all places you do have to ask for the discount. Even if they wanted to give it to you, it could be awkward for the cashier to ask someone how old they are, or worse assume someone is a senior who isn't, lol. So be sure to ask, and have proof of your age with you.
Don't forget to take advantage of these discounts, every little bit we can save helps nowadays. And those of you of a younger age, why not ask an elderly friend, neighbor, or relative to go with you, and use their discount. It can work out for both of you, as some elderly people find it difficult to drive themselves to stores. You'll both feel good for helping each other out.