Simplify the following text for a Grade 7 native English-speaking person.
Original: Within 24 months of the first ejaculation , the semen volume and the quantity and characteristics of the sperm match that of adult male semen .
Simplified: It either has no sperm in it , or sperm that do not move properly or do not move at all . A boy 's semen only becomes like an adult man 's semen about two years after his first ejaculation .