As long as you can reach the controls safely you can begin your flight training at any age you want.
But to fly solo without anyone else in the Helicopter with you, you need to be at least 17 years of age to get a private pilots license and to get a commercial pilots license you have to be 18 years of age or older.
You have to pass a written test on flying the helicopter and pass the actual test of flying the helicopter both with an examiner and then by yourself before you can get the pilots license to fly the helicopter.