According to Children’s Memorial Hospital, in normal puberty, the hypothalamus (part of the brain) sends a hormone to another part of the brain called the pituitary. This hormone stimulates the pituitary to make two different hormones.
These two hormones, in turn, stimulate girls’ ovaries to make androgens and estrogen and stimulate boys’ testicles to make testosterone.
KidsHealth.org said this causes breast development, pubic hair growth and menstruation in girls. Boys grow pubic and facial hair, have growth spurts, and their penis and testicles enlarge. Puberty generally begins between ages 7 and 13 for girls, and between ages 9 and 15 for boys.
Delayed puberty is when puberty begins later in a child's development than is typical, wrote About.com.
Lucile Packard Children’s Hospital at Stanford (LPCH) listed symptoms of delayed puberty in girls to include lack of breast development by age 13; more than five years between breast growth and menstrual period; lack of pubic hair by age 14; and failure to menstruate by age 16. In boys, there will be a lack of testicular enlargement by age 14; lack of pubic hair by age 15; and it will take more than five years to complete genital enlargement.
There are several reasons for delayed puberty. Children’s Hospital Boston said in around 60 percent of boys, delayed puberty is caused by constitutional growth delay (CGD). CGD is a temporary delay in skeletal growth.
In other cases, Children’s Memorial Hospital said boys and girls have pituitary and/or hypothalamus problems. The brain isn’t able to make hormones needed to start puberty. The ovaries and testicles work normally, but they never receive the brain’s signals to start making puberty hormones.
Problems with ovaries and testicles are another cause, continued Children’s Memorial Hospital. Here the brain senses the ovaries and testicles aren’t making the necessary puberty hormones. However it doesn’t know why, so it continues sending signals to the ovaries and testicles trying to get them to work.
KidsHealth.org stated that some with delayed puberty have chromosome problems.