Many websites I saw say that "adjectives that function like nouns" (the + adjective) refer to a group of objects, not a single object. For example, from The Britannica Dictionary:
She gives money to the poor.
Nurses care for the sick.
The words poor and sick here are used to refer to poor people and sick people, ... A lot of adjectives are used this way, many referring to classes of people ...
My question is:
Is it possible to use those adjectives to refer to a single object?
A young man and an old man in the park. The young is John and the old is Tom.