At 5'9 AT 14 you are definitely tall enough to play hooker. You might want to put on some weight and develop your strength and power. If you are looking for good rugby specific fitness and conditioning information go on If you sign up you will have free access to their software platform. You can set your fitness objectives, design a custom training program, schedule your session and take fitness tests to monitor your progress. The platform is in development right now but you can already use it and learn more about professional rugby preparation, fitness, nutrition and recovery. Some very simple tips: For full-body strength do Squats. For upper body, do clean and bench press, You are only 14 so maybe talk to a fitness and conditioning specialist first -- just to make sure your weight training program will not prevent your natural physical development. Work on your speed and agility as well: Hills sprints are very good for acceleration.
Extra protein &carbs in your diet. Heavy weightlifting (squats &bench presses).