a preemie
= a preemie is baby that is born ‘prematurely’ – before it has completely developed in the mother’s womb. Generally it takes 37 weeks/9 months for a baby to fully develop, so if a baby is born before 37 weeks/9 months, it’s considered a preemie.

 

a newborn
= a baby that was just born; this term is usually used for the first 4 weeks of life.

 

an infant / a baby
= the first year of life (from birth to 1 year old); an infant is a baby who has not started talking or walking yet and who needs constant care.

 

a toddler
= a child who is learning to walk; the 2nd year of life (generally between 12 months and 2 or 3 years old)

 

a child
There is no set age definition of ‘a child’; ‘childhood’ can be both the time before someone becomes a teenager and the time before someone become an adult. Most of the time, it refers to someone younger than a teenager.

 

pre-teen / tween
= around 10–12 years old; a child who has not yet reached the ‘teenage’ years. ‘Tween’ is short for ‘in between’!

 

a teenager
= someone who is 13–19 years old (any number with ‘teen’ in it!)

 

an adolescent
= a formal term for the teenage years; someone who is becoming an adult.

 

a young adult
This is hard to define! Generally someone becomes an ‘adult’ at the age of 18, but nowadays people are taking longer to mature into the adult years! A young adult could be anyone over the age of 18 but before ‘middle age.’ Most of the time a young adult is someone between the ages of 18 and 24.

 

middle-aged / over the hill (adjectives)
Since people are living longer, ‘middle age’ is changing. Generally, ‘middle–aged’ is the term for someone in the middle of their life, around 40–50 years old. “Over the hill” is a humorous (sometimes insulting) way of saying someone is old!

 

a senior citizen
= a polite way of saying ‘an old person’! The age at which someone becomes a ‘senior citizen’ can vary from country to country: it could be 55 years old, or it could be 65 years old!

 

elderly (adjective)
= a polite way of saying that someone is very old!