I wrote an (unpublished) novel, an epic fantasy in the vein of Lord of the Rings. There's a lot of world-building involved. The setting is an imaginary world with a level of technology of Greece in about 300 B.C. The world also has real magic, dragons and other species such as elves. In the story, people of all walks of life gather in a public square where philosophers offer free lectures. The following is an excerpt (slightly condensed here for clarity) of one of those lectures, given by an old philosopher by the name of Cogitson, who is discussing illusion (which is one of the themes of the novel).

Would you be so kind as to help me evaluate the following:
1) Is the philosophy believable and rigorous?
2) Is it appropriate, approximately, for the time period?

Please forgive the formatting - I'm not sure how to indent here.

“Life is but an illusion!" old Cogitson began. "Hear me: time is infinite … our lives are but a drop in the ocean of time. Even the span of the life of an elf is nothing compared to the ne’er-ending length of time. Even the so-called “long” life of a mage, extended by the artificial means of magic, cannot even begin to compare with the age of God! I used to call myself a wizard, a healer. I am two thousand two hundred and forty eight years old. But my life, as long as it may seem, is but a short dream. When I awake from this dream, I will return to the infinity. I will return to reality. We think we understand reality. But we understand so little. We are ignorant. The ant seems small to us, but the ant seems big to the mite.”
Cogitson held up a stone.
“What shape is this stone? Hmm?”
He held it out to a young man.
“Round,” answered the young man.
“To us,” Cogitson saith, holding the stone aloft, “It appears round. But what if a mite walked along the surface? Would the surface seem round to the mite? Or flat?”
The old philosopher paused and then tossed the stone to the ground.
“We have always assumed,” Cogitson saith, walking slowly in a circle, “that the surface of the world is flat … but perhaps our eyes deceive us! Perhaps … the world is not flat.”
Some of the people in the audience smiled.
“We know,” the philosopher saith, pointing his index finger up, “that elves can see more colors than we can. If an elf looked at, o … me, for example, he would see different colors than thee.”
Cogitson stopped walking.
“So, I pray thee: what colors am I? Does the elf see my true colors, or do we?”
He paused.
“The elf, because their eyes are better,” offered another young man.
“Ah … so a man with healthy sight will see the true colors of a thing, whereas an older man with weak sight doth not?”
The young man averted his eyes.
“T’is saith that a dragon’s eyesight is even better than an elf’s. Does this mean that the dragon sees reality as it truly is, whereas the elf does not?”
Cogitson paused and glanced around, slowly turning from face to face.
“Both are correct,” saith the prince. “And both are incorrect.”
The old philosopher smiled.
“Thou art correct, my prince,” Cogitson saith, with a little bow.
“Life is illusion,” the philosopher saith, pausing for effect. “Only God knows the truth of it. We can only hope to understand a small fraction of the truth.”
Cogitson placed his hand near his heart.
“We should be humble in our views of the universe and of life.”
Cogitson bowed more deeply.
“I thank ye.”