in terms of limits, at 50 you can do wakestyle, airstyle strapless, megaloops, whatever you want. Start off wearing straps, boots can let you catch an edge. You don't have to be that fit to kiteboard, it's like skateboarding in that way, except skateboarding is a lot harder on the body because concrete hurts more when you crash, in kiteboarding you just splash in the water. Kiteboarding is a lot less extreme than wakeboarding, in wakeboarding you are going faster and slam harder. Wakeboading is also a lot harder on the knees.
Airstyle is especially gentle on the body. It looks extreme to hit a big air and do a board off but really all you do is go up and land gentle as a feather, if you bomb you just throw the board behind you and splash.
It's your choice, airstyle, wakestyle, strapless, surfboard, waves, butter, your age is not a restriction.
as a beginner you will want to limit the top speed you go out in. If it is nuking, stay safe, don't ride. But that has nothing to do with being 50 it's all about being a beginner. Strong wind is what is dangerous to a newbie (30+ knots) not any particular style and not any particular age.