Can i apply androgel to accelerate my very sparse facial hair though my complte medical examination turned out fine except for obesity (bmi=37) age=18?

Weight loss: Adipose tissue (fat) can promote the formation of estrogenic (female) hormones and this decreases the affect of male (testosterone) androgenic hormones. I don't believe that using external testosterone would be recommended for an 18 year-old. Although, slower and more difficult, weight loss would correct this effect.

No: Androgel and testosterone replacement therapy is indicated for treating men with congenital or acquired androgen deficiency. Unless your total testosterone level is below 300 ng/dL you should NOT use these drugs.