The answer for the eldery is the same for all people with a couple of few small exceptions.
First and foremost protein intake should be parallel to the amount that you need. If you are sedetary you do not need as much as if you are active or doing weight training or things that require greater protein content.
Most elderly people are less active and do not do much exercise or weight training and therefore the amount of protein should vary. Most research will say around 1g of protein per kg of weight. Lets say you have an elderly person, if you use that standard (and most elderly people will lose weight) would put them at around 70g per day.
If someone is elderly and has difficulty chewing food or very inactive then I could see in the range of about .8g per kg, but if they are more active or involved in resistance training (which they should) or more strenous activity then that number could jump to 1.2g per kg.