Most healthy people with correctable eyesight, normal hand-eye coordination, no major health issues, proper motivation, and average or above-average intelligence can be trained to fly a helicopter.  Some learn quicker than others.  Some exceptions are people with severe motion-sickness problems, certain physical or mental handicaps, or an extreme fear of flying (some fear of flying is normal).  A fear of heights is NOT a problem; believe it or not, many pilots are afraid of heights.