If you love animals but are not able to care for one, or live in a facility which won’t allow you to own one, consider volunteering at an animal shelter. I work in the cat adoption room at Chicago Animal Care and Control and I get to play with and pet some very lovely cats, which they say lowers blood pressure. If you are a dog person, you can take dogs out for walks and play with them outside, or teach them basic commands like sit, stay and heel, which will make it easier for them to be adopted.
I have heard and/or read that grandparents like the fact that they are able to interact with their grandchildren but don’t have to live with them and working with animals at a shelter would be similar. You get the benefit being with them provides both of you, but the animal does not have to come home with you.
If you can have animals, but don’t want to commit to one for a lifetime, (theirs or yours) please think of fostering. While it may be hard to say good-bye to those you become attached to, you will prepare them to be better housemates and can provide potential adopters with valuable information about the animal’s personality and behavior.