Ellie is 6 and she plays all the time. Sometimes she sleeps because she likes to play with people and if I'm ignoring her, she just naps.
If I start playing ball or she brings it to me and I agree to play, she does for about 10 or 20 minutes and then rests awhile. She could play rest play rest play rest all day. If she is bored (which is often), she will bark out the window to entertain herself or beg for food.