ON Day 3 of the Winter Olympics, America’s biggest victory might very well have come not on a frozen halfpipe in China, but in the warm waves of the Banzai Pipeline, thousands of miles away in Hawaii. The win belonged to Kelly Slater, the surfing great who turns 50 this week. Slater defeated a rider less than half his age to capture one of the sport’s iconic events, the Billabong Pro Pipeline near the renowned reef off of Oahu. Now that he’s on top—again—Slater is starting to consider retirement. Nothing official, of course. Just thinking about it. For advice on the matter, Slater messaged wit…