unrelated; doesn't matter; no concern — a colloquial way to say something is irrelevant or not one's concern.
そんなことは私には関係ない。
That doesn't concern me.
気にするな。関係ないよ。
Don't worry. It doesn't matter.
それは仕事の外の話だから、関係ないだろう。
That's outside work, so it's probably irrelevant.
年齢は関係ない、やりたいことをやればいい。
Age doesn't matter; do what you want to do.