We started at nine years old and it was amazing to see how much quicker their feet can get from doing speed drills, cone drills, and rope drills. I would stay away from any load bearing exercises (weights) until they hit puberty but sit ups and push ups to strengthen the core are good at any age. Doing the speed and agility classes with the rest of the team helps them learn to push each other and support each other which carries over to the field.