At what age can a child start to work out with weights?

Depends: The aap & sports medicine groups encourage a delay in power lifting/heavy lifting until skeletal maturity. This varies with each kid & generally equates to final height & pubertal stage. Lifting technique and exercises with lower weight loads can be started earlier under the supervision of trained coaches. Such limitations are meant to reduce the rate of injury in each age group.

Until puberty begins: Once puberty is underway, a young boy or girl can do resitance exercise. Complete skeletal maturation is not a requisite. Before puberty, a younger child can do resistance excercises with their own body, ie climbing rope, pushups, situps, pullups. If a person weights till puberty, the trophic hormones present will enlarge muscles quickly; before their is a toning , but strength gain is much less.