Eat meat & vegetables, nuts and seeds, some fruit, little starch and no sugar.
Keep intake to levels that will support exercise, but not body fat.
Practice and train the major lifts:
Deadlift, Clean, Squat, Presses, Clean and Jerk and Snatch.
Similarly, master the basics of gymnastics:
Pullups, Dips, Rope Climb, Push Ups, Presses to Handstand, Pirouettes, Flips, Splits and Holds.
Bike, Run, Swim, Row, etc… Hard and Fast.
5 or 6 days per week mix these elements in as many combinations and patterns as creativity will allow.
Routine is the enemy.
Keep workouts short and intense.
Regularly learn and play new sports.