For a business to be successful, it needs to have customers. With the booming population of senior citizens, there are a lot of businesses that can easily provide services to that demographic, taking care of things that seniors might not have the ability or the desire to do in their later years.
Senior citizens often have a pet for companionship. However, many times seniors either can't walk very well or very far. If they have a dog that's still fairly young and energetic, then that dog needs to get out and walk every day. Many times seniors will be willing to hire a dog walker to take care of this chore for them. If you happen to like dogs, don't mind a little inclement weather, and you want to perform a service for seniors that they have trouble doing on their own then this might be a good business start up.
While it might be more than a little insulting to call your business a senior day-care center, there are a number of businesses that provide a communal place for seniors to get together. These centers often host activities for the senior community, and they provide staff that can provide supervision and care for their aging clients. The specifics of the center are up to you, and whether you'd rather have a bingo night or watch sports games on TV is up to you.
Just because a person gets older it doesn't mean they don't want to get out of their house from time to time. What it might mean is that they have trouble doing that on their own. If a senior doesn't have a driver's license, or they're physically impaired in some way (such as legally blind or wheelchair bound), then they may have to rely on family members or public transportation. You could easily provide a transportation service for seniors, and if there are a lot of seniors in the area you'll have a large population of potential customers.