Re: what age does sperm enter a young man's body?

Todd:

Boys are born with the cells which will make sperm in a very undeveloped 
stage.  These cells found in the testes are called spermatogonia and they 
will eventually produce all the sperm cells the man will have.  Around the 
time of puberty (http://www.youthshakers.org/sexualhealth/youngmen/), the 
spermatogonia will begin to change and start the process of sperm 
development called spermatogenesis 
(http://www.gpnotebook.co.uk/cache/892665869.htm). This usually begins 
sometime around 10-12 years of age and is fully functional by the age of 
14-16 years.  As the boy continues to mature, the number of sperm cells 
increases from few at 10-12 with a full complement of sperm cells by age 
16.  It is possible for very young boys to father children as the number 
of sperm in sufficient at puberty to fertilize oocytes. 

I hope this helps!!

David Mallory, PhD
Marshall University
Huntington, WV USA