even for delayed puberty 20 is very low. I started puberty late, around 17~ just starting to get facial and body hair at 23, TMI, even grew an inch this past year.
Anyways You really need a full panel before you proceed to rule out the issues. We want to make sure your thyroid is healthy, growth hormone is okay, cortisol and estrogen are fine. We need to rule this out to find out why your testosterone is at the level of a pre-pubescent woman.