QuestionI do not have armpit hair yet. I have pubic hair and I can produce sperm. My penis is still small though. When will it start growing?
You didn't give me enough information to give you a detailed answer. I would need to know what stage of development you are in (see: The Tanner Stage of Development Calculator). My guess from what little you stated is that you are in stage 2 of development. The penis increases in length during your growth spurt, which happens in stage 3. It increases in circumference during stage 4, which will be the stage when you start to notice underarm hair.
Some try to gauge the size of their penis based on its flaccid length -- that is, the length when the penis is not erect. There are problems with this: the flaccid length of a penis changes with temperature, blood pressure, and state of arousal. A man's penis in the flaccid state constantly changes size.
Another problem is that the flaccid length of a penis does not directly match the size of the penis when erect. A large flaccid penis often becomes erect with only some increase in size, while a small flaccid penis can dramatically increase in size during an erection.