二つ下のいとこ instead of はとこ


I'm trying to understand the usage of 二つ下 in the following sentence.

シンちゃんは私の二つ下のいとこです

When I read it without 下 it sounds like:

Shin-chan is my second cousin or something along those lines.

The issues is I don't understand the usage of 二つ let alone 二つ下 in this
sentence.

Wouldn't it usually be written as シンちゃんの私のはとこです

I'm a bit confused here.




In 明鏡’s definition for 下:

> ❺ 地位・能力・程度・ **年齢** などが劣っていること。また、その人。 「3歳下の弟」

Namely, 下 can refer to the fact that someone’s position, ability, level, or
age is lower. In your case it’s age.

In the example it uses 歳 instead of つ for the counter, but つ (as well as 個)
work for age just fine, albeit slightly informal.




In 明鏡’s definition for 下:

> ❺ 地位・能力・程度・ **年齢** などが劣っていること。また、その人。 「3歳下の弟」

Namely, 下 can refer to the fact that someone’s position, ability, level, or
age is lower. In your case it’s age.

In the example it uses 歳 instead of つ for the counter, but つ (as well as 個)
work for age just fine, albeit slightly informal.

