Whitman suddenly becomes excited again thinking about youth and manhood.
He feels as though he has lovers coming to him at all hours of the day, "crowding" to kiss his lips and to find him in the streets.
He thinks old age is "graceful."
When he looks at the sky at night, he sees the universe expanding in every direction, "outward and outward and forever outward." Expansion and circles are a huge deal for Whitman.
The world cannot condense; it has to keep expanding and moving further.
In various ways, he describes the limitless nature of the universe and how everything is just a small part of the pattern.
At the end of the section he says that the date of our final "rendezvous" has been set, and God will be waiting for us. He's talking about death, but in cryptic terms. Maybe he means that after death we will have a sense of the universe as a "whole" rather than a collection of "parts."
Then again, Whitman doesn't seem concerned with what happens after death, he just doesn't think we should worry about it.