I usually don't do much with my elders, as they tend to have grown or almost grown kids by then, so I tend to start focusing on the next generation once they start coming of age, so I've been making an effort to pay more attention to the elders in my game. I tend to just let them continue what they've been doing, usually working and hanging out with friends and family. I always make sure to introduce them to any grandchildren, nieces, and/or nephews they might have.
In my current rotational save, one of the families is made up of a husband and wife and their teenage daughter. The parents are adults at the moment and work as self-employed archaeologists who live in Selvadorada. Once they become elders, I'm going to have them "retire" and move back to their house in Willow Creek full-time. To give them something to do, I'm going to have them authenticate items they receive in the mail and give archaeology lectures around town.
Another of my families consists of Bernard Shaw (from the Von Haunt Estate) and his girlfriend, Violet, one of my sims who was born in-game. Bernard doesn't seem to age, but Violet does, and she's very close to becoming an elder. I'm going to let her continue working her job and having her visit her son, daughter-in-law, and granddaughter. I'm also planning on having her take in her younger cousin (who's a YA), who doesn't want to live in a house full her two brother's kids.
Another of my elders lives with one of his cousins and is helping her raise her three kids. She was forced to move out of her wildly expensive lot and into something cheaper, so he invited her to live with him and help out as much he could for as long as he could.