Hello...... I think you should know that male genital size and length varies from person to person. A person can have less sperm count or impotence due to less testosterone level which might be a cause or disease affecting blood vessels supplying the genitals, certain infection, diabetes, neurological disease or spinal cord lesions, lesions affecting the part of the brain which helps in proper secretion of hormones responsible for growth of male genitals can be a cause....Trauma to the organ can also affect. Short penis is generally referred as penial length less than 2 inch, it is measured by certain standard techniques.... So kindly consult a urologist for further management.....