Eat, nuts and seeds, fruits and vegetables, some starch, little sugar. Keep intake to levels that will support exercise, but not body fat. Practice the major lifts: deadlifts, squats, presses, clean & jerk and snatch. Similarly master the basics of gymnastics: pullups, dips, rope climb, pushups, situps, presses to handstand, pirouettes, flips, splits and holds. Bike, run, row, swim etc. Hard and fast. Five or six days a week, mix these elements in as many combinations as creativity will allow. Routine is the enemy! Keep workouts short and intense. Regularly learn and play new sports.