Average Bmi Chart Below Recommened BMI?

Below recommened BMI? - average bmi chart

I am 19 years old with a thin, and I'm a little shorter than the average.

I checked the number of body-mass index, and over 17 (20 minimum recommened) and I wondered is ... What is fever?

I am in very good condition, I eat mainly healthy foods and I eat very often. I do not feel weak or sick, then how accurate is the BMI charts?