There is no fixed upper age limit, it depends upon the sex drive, activeness and attractivness of the individual. We run swingers parties every month, our oldest regular is a 72 year old man, and we have a lady in her early 70's who is very active at all the parties.
The lower age limit is fixed by laws in different countries or states.
The generally accepted minimum age for a guest at a swingers lifestyle club or party is 18, except where the age of consent is higher. If the age of consent is lower than 18, most clubs and parties still apply a minimum age limit of 18.
Even though a club or party may allow younger or older guests, there is no guarantee that they will get any action. Some people feel uncomfortable playing with people younger than their children. Some younger players feel wierd playing with guests old enough to be their grand parents.