"To die quietly of old age would be to go there on foot" is a less straightforward, more lyrical phrasing. It inverts the expected structure, which would be:
"To go there on foot would be to die quietly of old age."
The meaning of the sentence is that the journey would take so long on foot that a person would die before they reached the destination. The inversion here is a stylistic choice, also called anastrophe.
This link has some good examples of inversion, such as:
"To me alone there came a thought of grief" from Huckleberry Finn. A standard form of this same sentence would be "a thought of grief came to me alone."