why is it that old people are called old and...

That is because English is Funny. In Sinhala (Language of Sri Lanka) we call old "parana", but old people are not called "parana people". We progress from infancy al Bala, Thruna, Mediwiya and Mahalu. I stll remember the poem we used to study in primary school. It is called "Funny English" Funny English We'll begin with box, and the plural is boxes, But the plural of ox is oxen, not oxes; Then one fowl is a goose, but who are called geese, Yet the plural of mouse is never meese. You may find a lone mouse or a whole set of mice, But the plural of house is houses, not hice. If the plural of man is always men, Why shouldn't the plural of pan be pen? If I speak of a foot and you show me your feet And I give you the boot, would a pair be called a beet? If one is tooth, and a whole set are teeth, Why should not the plural of booth be beeth? Then one may be that, and three may be those, Yet hat in the plural would never be hose. And the plural of cat is cats and not cose. We speak of brother and brethren, But though we say mother, we never say methren. Then the masculine pronouns are he, his and him, But imagine the feminine — she, shis and shim! So English, I fancy, you all will agree, Is the funniest language you ever did see.

I think its just a matter of the choice of word. Old people means elderly people. But for young people noone will say new people :-) I think we should blame it to our ancestors who started the word "old people" and "young people". Maybe before the word "New" did not exist yet. So they started calling the not elderly people as "young people" instead.

Probably i dont know why?i also not ever thought abt it even.Its a good question.Will surely post u a msg if i get to know the answer lol