How to Say "Same Age" in Japanese

同い年

onaidoshi[o̞na̠ido̞ɕi]

The English phrase "same age" is translated into Japanese as 同い年 (onaidoshi).

同い年 is used to describe two or more people who were born in the same year. It can function as a noun or a noun phrase within a sentence.

How does it change in a sentence?

In casual speech, you can end the phrase with the copula だ (da) to state that someone 同い年だ (is the same age).

onaidoshi

Japanese culture has a specific term, 同期 (douki), for people who are the 'same age' in terms of joining a company or starting school, regardless of their actual birth date.
In Japan, being 同い年 often creates an instant social bond, leading people to use the casual タメ口 (tame-guchi) style of speech even if they have just met.
Japanese has a specific term, タメ口 (tame-guchi), for the casual speech style that 同い年 peers use, which literally translates to 'equal mouth'.

同い年だよ。
I am the same age.
Tatoeba #9388325 by small_snow, translation #259716 by CK
彼らは同い年だ。
They are the same age.
Tatoeba #96463 by small_snow, translation #307243 by CK
私と同い年なのよ。
She's the same age as I am.
Tatoeba #11831988 by small_snow, translation #9640501 by Ricardo14
彼は私と同い年です。
He is the same age as me.
私たちは同年代です。
We are the same age.
私たちは同い年っす！
We are the same age!
27 more sentences on Tatoeba

Kenta and Himari are talking about a new colleague.

健太 Kenta

田中さんは、陽葵と同い年なの？
Tanaka-san wa, Himari to onaitoshi nano?
Is Tanaka-san the same age as you, Himari?
陽葵 Himari

うん、実は同い年だよ。
Un, jitsu wa onaitoshi dayo.
Yes, actually we are the same age.
健太 Kenta

それは気が合うね。
Sore wa ki ga au ne.
That's good, you'll get along well.
陽葵 Himari

そうだね、仲良くするよ。
Sou dane, nakayoku suru yo.
You're right, we'll be good friends.

Sources

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