najstarszym

In a sentence

• Mój brat jest najstarszym członkiem naszej rodziny.

  My brother is the oldest member of our family.

  Here, "najstarszym" is used as an adjective describing "członkiem" (member), indicating the superlative degree of being old within a defined group (our family).

• To drzewo jest najstarszym w całym parku.

  This tree is the oldest in the entire park.

  In this sentence, "najstarszym" serves to modify "drzewo" (tree) in the superlative degree within the context of the park.

• Najstarszym znanym tekstem literackim jest Epos o Gilgameszu.

  The oldest known literary text is the Epic of Gilgamesh.

  Here, "najstarszym" operates in the superlative form to describe "znanym tekstem literackim" (known literary text) within the scope of known examples.