We cannot usually leave out a noun after an adjective.

Poor little boy! (NOT -PeeHrttlet-)
But there are some exceptions:

We sometimes leave out a noun when we are talking about a choice between two or three different kinds (of car, milk, cigarette, bread, for example).

Have you got any bread?¹ 'Do you want white or brown?
'A pound ot butter, please.' 'I've only got unsalted '

We can use superlative adjectives without nouns, if the meaning is clear.

I'm the tallest in my family. 'Which one shall I get?' The cheapest '

We can use some adjectives with the to talk about people in a particular condition.

He s collecting money for the blind.

Note that this structure has a plural 'general' meaning: the blind means 'all blind people', not 'the blind person' or 'certain blind people'.
The most common expressions of this kind are: he dead the sick the blind the deaf the rich the poor the unemployed the young the old the handicapped the mentally ill (In informal speech, we usually say old people, young people etc instead of the old, the young.)
These expressions cannot be used with a possessive's. the problems of the poor OR poor people s problems.

Food Facts
In China, eggs are buried underground until they go exceptionally bad and are then sold and eaten as ‘hundredyear- old' eggs. In fact, they are about two years old. The yolks turn green and the whites turn grey or black.      .. More >>