it changes state to state, where I live it is 17, but I think you may be able to at 16 with parental consent.
I tried at a blood drive at my school, but the vein collapsed. Then the nurse told me that was like the 4th time she had done that today. It made a weird bruise under my skin, and i felt this like pinching in my arm for a week or two, but hopefully it will work out next time i try