I thought lake Arlington was closed?
Anyway, I've had the same problem the past couple of seasons. I'm close to your age and really didn't get much in the way of exercise other than wakeboarding. I would typically take 2-3 sets each time out, but they would be 5-10 minutes tops for each set. I would get really winded and just plain tired because I was just so out of shape.
About two months ago I bought a knock off of "The Total Gym", you know, the one that Chuck Norris and Christy Brinkly sell. The knock off one I bought was from Weider; it cost a whopping $99. This thing isn't going to make you into a body builder by any means, but it does do a great job of stetching and toning.
I work out on it for 15 minutes everyday and then ride a stationary bike for 15 minutes each day as well. Since starting this routine my endurance while riding has at least doubled. I can ride much longer and also have a bit more arm strength than before which helps in keeping the handle in close.
My friends made fun of me for buying it, but so far it has made my wakeboarding much more enjoyable. Now I just need to start eating right and lose my gut!
Here's a link to the machine I bought. I can't say enough great things about this machine in regards to working alot of the same muscles used in wakeboarding:
http://www.dickssportinggoods.com/product/index.jsp?productId=1073982&cp=