The physical maturing that makes an individual capable of sexual reproduction.

The answer is Puberty

Explanation:

When humans reach Puberty, their bodies begin to develop further and change. In men, this can be seen by the growth of pubic hair, enlarged testicles, a deeper voice and the production of sperms.

In girls, this can usually results in growth of pubic hair, widening of the hips and monthly cycles of menstruation.

Once humans go through his process, they are capable of sexual reproduction. Men can product semen while women can produce fertile eggs that can result in pregnancies.