Always used in possessive form. 소유격으로 사용해야 합니다.

예시)

He’s in his teens.
She’s in her 20s.
He’s in his 50s.
I think he may be in his 80s.
They’re in their teens.

20대를 사용할 때는 20’s 가 아니고 20s 라고 표시 하면 됩니다.

단, 연도를 줄여서 사용할때는 아포스트로피(‘) 사용합니다.

I was born in the ’60s 60년대에 태어났어요 (1960 년을 줄일때는 사용)

No apostrophe after the zero, despite the fact that many native speakers make this mistake.

그는 10대야 (또다른 표현)

He’s a teenager.

그녀는 20대 초반이야 / 그녀는 20대 후반이야

She is in her early 20s./ She’s in her late 20s.

Twentysomething (또는 twenty-something)
Thirty-something
Forty-something

This priduct was especially popular with twentysomthings in New York.

청년층, 노년층
The youth, the elderly… (집합명사, 복수에 s를 붙이지 않아요)

The youth in Korea (한국의 청년들)

중년
Middle age, middle-aged
Once you hit middle age…(중년이 되면 )

A middle-aged man walked up to me on the street yesterday.

People in their 20s
People in their 40s
Respondents in their 20s cited financial insecurity as the number one cause of stress in their lives.