small clitoris, thick hood
I have a very small clitoris, and a thick clitorial hood. Also very large labia. Never had an orgasm until I turned 53 (with a vibrator, never with a partner). It is very difficult achieving orgasm, sometimes unsuccessful, even after trying an hour. It seems to take forever to "find the sweet spot" and them sometimes I remain on the plateau forever, never achieving the Big O. I would venture that I achieve orgasm 50% of the time.
Someone suggested that the small size of my clitoris along with the thickness of the hood could get in the way. Also, never having an orgasm until 53 could have some effect; i.e., the "connections" between the brain and the clitoris via nerves and blood vessels was never established.
Let me say that I have a very strong libido, and no lubrication/physical or psychological issues and take only vitamins and HRT/Testosterone. I have wonderful and loving partner.