Nestor does not really have an opinion about Odysseus other than that he remembers him briefly as a warrior. He remembers Odysseus from the end of the Trojan War but notes that they did not leave for Greece on the same ships, so he does not know what has become of him.
As Telemachus searches for Odysseus, he visits Nestor, the King of Pylos, in book three of "The Odyssey." According to Nestor, after the Trojan War ended, Greek brothers Agamemnon and Menelaus had a disagreement, so their forces left separately. Nestor left with Menelaus for Greece, while Odysseus waited a day for Agamemnon to finish his sacrifices and leave to return to Greece.
Nestor notes that he has heard nothing of Odysseus since, other than that in Odysseus' absence his castle has been besieged by suitors for his wife. To aid Telemachus on his search, Nestor sends his son, Pisistratus, to accompany him across land to Sparta. Telemachus is Odysseus' son. He was an infant when his father left for the Trojan War and is approximately 20 years old at the beginning of "The Odyssey." His travels through books three and four, including his encounter with Nestor and his developing the courage to speak to the king, display how Telemachus matures throughout the story.