I'm a freshman and I want to date a junior is that wrong? Cause I don't want to date freshman guys cause they are so immature.

Got anyone in mind? Dating is about attractions after all. As far as being wrong, that would be up to your parents, wouldn't it? What do they say?

My dad doesn't care as long as he is in high school still.

My dad doesn't care as long as the person is still in high school

I would not strictly limit the possibilities .

You may find the guy you are looking for anywhere and he may be younger than you.
It is a case by case type of search.