A lot of times when dogs cry at older ages is either because they are in pain or they want to be near you. I have a teenage dog so to speak and I have researched this due to his whining and crying. A lot of it is they want to be near you al the time and if the whining persists while you are in the room its because they want your attention, or like I said before they are in pain.
Because they know they are old and soon they will have to go and they want to enjoy every minuet they have left but if you have an old dog make sure to spend a lot of time wit her/him