Why am I balding at 18? (Photo)

It is possible that the influence of genes can skip generations. Also, it may be the case that genetic predispositions may be worsened by various environmental factors, such as unhealthy lifestyle practices, pollution, excessive sun exposure, nutritional deficits and more.
There are many possible contributors to early signs of hair loss. This includes inflammation of the follicles where the immune system is triggered by the presence of microbes, such as fungus or bacteria. Also stress which manifests as sudden physiological changes or shock can also cause the follicles to shed hair and enter a resting mode where hair production stops. This is usually temporary. Genetics (i.e. pattern baldness) is the most common reason for hair loss in most males. And hair transplantation offers the most reliable way to restore hair growth.  With the right diagnostic assessment to know the future course of hair loss and by planning for long term surgeries (i.e. head hair alone or the use of body hair), it is possible for younger patients to benefit from hair transplantation The gentleman in the video below was not 18 at the time of his transplant. But his case helps illustrate how it may be possible to undergo hair restoration surgery at a young age. 

Balding at the crown is typically related to genetics in males. I suggest you schedule an appointmentwith an experienced hair loss specialist who can take a detailed medical and family history andexamine the areas of concern.

Great question. I see more and more teenagers and young adults with hair loss. It could be related to Male Pattern Hair Loss (genetic). I won't recommend any treatment at the moment, and I will suggest you to make an appointment for evaluation/diagnostic/treatment options with a local and experienced hair loss specialist in your city/state. Good luck.