Periods of Life

Infant: Usually from birth to about 12 months (before they can walk).

Baby: a very young child (includes infants and slightly older children).

Toddler: 12-36 months (after being able to walk).

Preschooler: 3 - 5 years of age (a child not old enough to attend kindergarten).

Child: Between birth and Puberty (in the US around 11 for girls and 13 for boys).

Adolescent: Between the ages of 12 or 14 to 19 or 21 (in the US).

Teenager: From 13 to 19 years of age.

Adult: In most countries the legal definition is usually someone over the age of either 18 or 21.

Middle Age: Between 35 and 54 years of age (according to the US Census).

Old Age: Roughly after 65 years of age (this age group is also known as the elderly, seniors or senior citizens).

Centenarian: someone who has lived to the age of 100 and above.