Playing with the family, neighbors, friends, etc. Whenever we went outside, it motivated enough people to come out, that we had teams for sports. Yay!
The youngsters and old timers all get along and surprise each other with the level of fitness each one possesses.
Think outside the box when using a ball, frisbee, jump rope, etc. Group and partner drills, races, obstacle courses, etc.
How about a scavenger hunt, getting the person to search up and down the stairs, that is so much fun, too.