I'm 135lbs and 5'8" and I ride 190 Live Life 1s just fine, and they are incredibly stiff.
Yes, skill plays a phenomenal factor in distinguishing which flex/length is suitable, but riding a bigger (or stiffer) ski will definitely improve your riding, because more core strength and general muscle is required to achieve the same level of agility that you would have with a smaller, lighter pair of skis.
When I was 5'4" and 145lbs I rode 179 powder skis, which felt way too big at first, but after a week of riding on them I was able to control them just fine. I began noticing that I had more leg and core strength, as well as stamina. a few years later I switched from a light/soft park ski to a super stiff/heavy park ski, which again helped me A LOT with my skiing strength.
People in the 80's were doing triple flips on 200cm skis that weighed ten times as much as modern skis, and you think he can't ride a bigger ski? A good skier can ski any length.