Motorcycle Safety & Driveability: age wise for bikes, 125cc dirt bike, professional rider

Question
what age would you prefer a 14 year old thats 5 feet should begin on a 125cc dirt bike that seat height is 36 inches

Answer
It really depends on the rider.  Is he/she able to comfortable control the bike?  Will they undertake a professional rider instruction course? What previous riding experience do they have?  These are the questions which need to looked at to make the decision.

Cheers