Get to the weight room and begin working on your core strength. Also work the legs (leg presses / extensions / curls) and the back (chest pulls / bent rowing / etc.). Don't forget the chest (bench press / push ups) to balance the back work. You may need some help from a trainer to get started, but it will be worth it. As you increase muscle mass, your matabolism goes up and your weight loss improves. Plan on at least 2 and if possible 3 workouts a week. Full body workout each time with at least one day recovery/rest between workouts. Use it or lose it! Life gets better with age.
Learning to windsurf is much easier these days, but it still can be frustrating at times. PERSIST - it will be worth it.
I am 63 and have been windsurfing for 24 years. I am in excellent shape because the windsurfing motivates me to be ready to hit the water at any time. I sail all year long and live in north Texas. I average 50-60 sessions / days a year. I would be out more, but I still have to work.