19-year-old male with 21.5% body fat?

Is this normal, or would I be considered fat? I run all the time, I'm really skinny and you can see my abs coming through. Yet extreme fitness told me today that I have 21.5% fat today which seems high to me. Is it maybe because I have a lack of muscle and a skinny frame? Should I tart lifting weights and maybe that will lower my body fat %?