Spermarche
Spermarche, also known as semenarche, is the time at which a male experiences his first ejaculation. It is considered to be the counterpart of menarche in girls. Depending on upbringing, cultural differences, and prior sexual knowledge, males may have different reactions to spermarche, ranging from fear to excitement. Spermarche is one of the first events in the life of a male leading to sexual maturity. It occurs at the time when the secondary sex characteristics are just beginning to develop. Researchers have had difficulty determining the onset of spermarche because it is reliant on self-reporting. Other methods to determine it have included the examination of urine samples to determine the presence of spermatozoa. The presence of sperm in urine is referred to as spermaturia. Age of occurrence 
Research on the subject has varied for the reasons stated above, as well as changes in the average age of pubescence, which has been decreasing at an average rate of three months a decade. Research from 2010 indicated that the average age for spermarche in the U.S. was 12–16. In 2015, researchers in China determined that the average age for spermarche in China was 14. Historical data from countries including Nigeria and the United States also suggest 14 as an average age. Context 
Various studies have examined the circumstances in which first ejaculation occurred. Most commonly this occurred via a nocturnal emission, with a significant number experiencing semenarche via masturbation, which is very common at that stage. Less commonly, the first ejaculation occurred during sexual intercourse with a partner. See also 
Adrenarche

References 

Developmental biology
Developmental stages
Human male reproductive system
Puberty
Sexual health
Sexuality and age
Men's health