How is it that a person that is 21 can not have temporal arteritis even if they r feeling symptoms close to that problem?

They could : But it would be very unusual or rare. So your evaluation will look first for more common things for your symptom complex and other factors.

It is!: Despite your symptoms, temporal arteritis is not just clinical term, but also requires hard data (increased crp, evidence for arteritis by biopsy, or mra). If the basic data are missing, then you don't have it! than god for not having that dx.