From birth, babies can experience sexual pleasure from touching their genitals and males can have erections. By around age 2, infants will know their own gender and understand the difference between male and female genetalia. As they get older they will become more curious about sexual subjects.
Pre-adolescence usually occurs between ages 8 and 12 and children will become more self-conscious about their bodies. They will also experience some changes to their bodies including the growth of pubic hair, larger testicles in males and breast buds in female. They will become more interested in sexual subjects and may masturbate although the thought of sexual intercourse is often an unpleasant one.
During the teenage years, children experience puberty as their bodies mature in adulthood and their primary and secondary sexual characteristics develop. Females will experience menstruation and masturbation for both genders will be common. Teenagers will also become more interested in forming romantic and sexual relations.
During adulthood, most people will have a desire for intimate and sexual relations and may wish to have children.
At around age 50, women will experience the menopause, indicating the end of their ability to have children. This may also reduce their sexual desire. Men may also have a reduced desire for sexual relations and may find it more difficult to maintain an erection although they may still be able to father children.