adjectives are always singular in english

Yes, but this only applies to a few adjectives which refer to particular social or demographic groups of people. For example: the poor the rich the young the old the sick the unemployed In these cases, you can use an adjective preceded by the definite article to create a noun referring to a whole category of people. For example, "the young" means all young people. Two things to bear in mind: There is only a limited number of adjectives which work in this way. Referring to people in this way is rather formal and possibly somewhat outdated.

Give us an example of what you mean.