My penis, when flaccid, has not grown. It looks same as from when I was little (about an inch). I am 15 years old. When I am erect it is 12.5 cm long. It has grown 2 cm from two years ago. I took the test and I got 2.9. Is this normal for a penis to be so small when flacid? At age 15?
We always discuss a man's erect size and not his flaccid size because the size of a man's penis varies greatly when flaccid. If you are cold, it will draw up to conserve heat. If you are hot, it will expand a bit to give more cooling. When you get erect, your penis expands like a balloon. Some men start small and it expands a lot -- you sound like you are in that group. Other men start out bigger, but their penis only gets a little bigger when they get erect.
The normal range for adult males is between 8 and 20 cm. The average is 13 cm, so you are just a little bit below the average and you haven't even finished growing yet. If your answers were accurate, then you have not yet had your growth spurt and it is during the growth spurt that your penis gains the most length. Then after the growth spurt slows down, that is when your penis gets bigger around.
The average age to have a growth spurt is 13, so at 15 you are slightly behind other boys your age, but you are still within the range of normal.