Final answer:
Mature sperm is found in boys' ejaculatory emissions during late adolescence.
Step-by-step explanation:
Mature sperm is found in boys' ejaculatory emissions during late adolescence.
According to research, boys generally start producing semen around the age of 13, which may contain some sperm even though full fertility is not achieved until later in adulthood.
Puberty in males usually begins between the ages of 11 and 12 and continues until around the age of 18.