I would check with your insurers but we cannot offer hair colouring services to anyone under 16 years due to regulations introduced a few years ago around (colour) chemicals and the risk of causing lifelong allergies in developing bodies. All hair colour products must contain a warning advising not for use by someone under 16yrs, including box colour dyes.
Personally, as someone with a severe allergy to methacrylates, I would stick to the 16yrs limit.
Methacrylates are used in lots of applications but particularly in the medical profession, and if a client develops an allergy, it can affect the treatment options available to them.