Grew up golfing on a short, very simple 9-hole course in North Dakota. One gorgeous day me and a buddy were for some reason just about the only people there, I think we saw 6 other people the whole day so we never had to wait to hit. We started just after noon, flew through the first 9 holes and kept going.
Most holes were a driver and a wedge, so we didn't have to spend any time picking a club....knew the greens like the back of our hand and they weren't terribly complex to begin with. Already knew what we hit into every par 3. Just kept playing......and playing......never rushing just playing ready golf with one cart, could pull right up next to every tee and green. Both of us were playing well, par was 34 and we were both consistently shooting 35-37 all day.
Around 8pm we called it a day, counted the score cards....we had knocked out 90 holes in just under 8 hours. ~45 minutes per round for 10 rounds. Youth is a fantastic thing because my current lower back surrenders about 5 minutes after finishing 18 these days.