Younger and older

Hi, today, I'd like to clarify my possibly wrong concept for words 'younger' and 'older'

Since I heard them in american drama, the meaning of them were fixed to me young people and old people.

I don't know if they have 'the' in front of them: the younger and the older

Are they just like the the + adjective such as the poor and the rich? that are considered as a noun? (poor people and rich people)

If this is all wrong, it'd be good to know a shorter or another form of young people and old people.

I hope the question I made is not confusing ?.?