Fetal period: From conception to birth (approximately 40 weeks of gestation).

Neonatal period: From birth to 28 days after birth.

Infant period: From the 29th day after birth to 1 year old.

Toddler period: From 1 year old to 3 years old.

Preschool period: From 3 years old to 6 years old.

School-age period: From 6–7 years old to puberty (13–14 years old for boys, 11–12 years old for girls).

Puberty: Boys aged 13–14 to 18–20 years old; girls aged 11–12 to 17–18 years old.