There are various types of dirt bikes and various ways to use them. You should have the one that fits your needs.  The brand and model are your choice but the size and use is based on you.

     As you can see there is a picture to the right and it is a 9 year old racing a KTM Sx 65. This bike is the perfect size for him. It is not too big or too little. You will also notice that he is wearing the proper gear for what he is doing.

The helmet is the most needed piece of equipment for riding dirt bikes. Boots, gloves, chest protectors, shirts, pants, and kidney belts are all things that are unnecessary but will help.