I'm 14 and I have minor bald spots on my head. Can I use a hair regrowth treatment to grow back hair in those bald spots?

You need to first find out why you have bald spots and why you are losing hair.  This generally requires an examination by a doctor.  If you have a diagnosis, you can consider treatment options.Bald patches can be Alopecia Areata, Lichen Planopilaris, fungal infection, or other medical conditions which all have different treatments.

You need to see a dermatologist to determine your diagnosisAloepcia areata, fungal infections, trichotillomania are top causes of hair loss in 14 year old male. Other causes are poosible too, albeit less commonThe only way to figure out how to treat your hair loss is to first determine the diagnosis.Please see a dermatologist. 

before using any products, you need to find out the cause for your hair loss. It is best to see a specialist for a diagnosis and proper treatment options. 

This can be caused by many conditions including a fungus, a disease called alopecia areata, etc... What I am saying here is see a dermatologist and then you will get a diagnosis. There is no substitute for seeing a good dermatologist.

You need to be seen by a dermatologist to have your condition properly diagnosed in order to  come up with a treatment plan.