I’m 67 yo now and start better than I did 20 years ago. Agree with comments above, flat ski, start from “in gear” not dead stop, etc. I will add to “engaging your core” to “engage everything”. I tell people to make like you are a statue and the boat will pull you up. Don’t fight it. Also, when going calling for “in gear”, if you are in the correct position relative to your ski and the water you should notice that you will rise up ever so slightly as you gently move forward. If you don’t, or if you start to go down lower in the water, you are definitely not in the correct position. Finally, if you are wearing fashionable baggy swim shorts, swallow your pride and get some skin-tight shorts. This will reduce water resistance and make it consistent. With the baggy shorts, sometimes it felt like an open parachute in the water; sometimes not. Switching to tight shorts was one of the best things I did to have consistent easy starts.