I guess it really comes down to how healthy they are. Are they like actress Betty White, age 90, or Tony Bennett 85, working and getting around fine? Another factor to consider is where they are located. Some folks enjoy a nice morning walk to have breakfast at a local restaurant or even to sit and drink a cup of coffee at a bakery or McDonalds.
If there is a park nearby they may enjoy walking around it and if there is a small pond with pedal boats they might spend an hour or so cruising along. Another possible activity is volunteering to be a senior activities director at a local senior center or nursing home.
If there is a movie theater close by they can go see a matinee. Last but not least they can check the local paper to see what activities are planned for seniors in their area. Most towns and communities offer free or low cost activities for senior citizens. Public libraries also have lists of local activities.
However it all comes down to health and (desire). Some people young and old don't want to leave the house, meet other people, or become engaged in any activity other than eating, sleeping, and watching TV. It's important to remember that (life is a personal journey). As much as we might want something for those we love, if they don't want it for themselves then we must accept that their life is theirs to do with as they please. Just because we might feel we'd be unhappy in their situation does not mean (they) are unhappy.