Water skiing is so easy to learn, if you have a pair of wide combo skis and someone who knows how to teach a beginner. My 30 year old co-worker who came to visit one weekend up at the lake this summer had never water skied her in her entire life. She was able to get up and have a blast skiing, I think it took her 2 or 3 tries.
Obviously skiing faster and on a slalom ski, especially if you're running a course, is harder, but a double black diamond run is harder than the bunny hill.
We even had my cousins' kids who were 4 and 5 skiing behind the boat, (and a 2 year old on the easy ski) you don't have to go fast to ski. No they didn't ski 6-7 hours a day, but when they go snow skiing they don't last very long on the bunny hill either.