In Cormac McCarthy's novel All the Pretty Horses, what is meant by the phrase "ten thousand worlds for the choosing"?

In Cormac McCarthy’s “breakthrough” novel All
the Pretty Horses, the phrase “ten thousand worlds for the choosing” appears
on page 30 of the first American edition. John Grady Cole, the young main character, and
his young friend Lacey Rawlins are on horseback, heading toward Mexico on a dark,
starlit night. McCarthy writes that

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they rode out on the round dais of the earth
which alone was dark and which carried their figures and bore them up into the swarming
stars so that they rode not under but among them and they rode at once jaunty and
circumspect, like thieves newly loosed in that dark electric, like young thieves in a
glowing orchard, loosely jacketed against the cold and ten thousand worlds for the
choosing.

The phrase “ten
thousand worlds for the choosing” refers most obviously to the stars, which seem to
surround the young men, so that they almost seem able to reach out and touch one of
these “worlds.” More figuratively, the phrase suggests that these young men seem to have
limitless potential and enormous opportunities at this stage of their lives. They are
young; they are strong; they have not yet faced any major challenges or dangers; and
they are off on a journey that does not intimidate or worry them. They are
self-confident, archetypically adventurous young men. The symbolize that phase in life
when all paths seem open, when we seem to have nothing but attractive choices before
us.

Of course, the tone of the novel will change
dramatically later on. Nature will not seem as friendly or beautiful later as it seems
on the night described here. John Grady and Lacey will undergo the archetypal process of
initiation into a world of love, loss, death, and maturity. For the present moment,
however, they seem to have their pick of possible worlds to choose
from.

Nevertheless, hints of what is to come are contained
in this passage. Here the young men are metaphorically described as thieves; later they
will be accused of actual thievery. Here the two young men seem to move amidst a
star-filled sky without taking very great notice of their beautiful surroundings. Later,
John Grady and Alejandra, with whom he falls in love, will deliberately go into the
hills to admire the beauty of the stars (140-41). Here the stars seem like golden fruit
ripe for the picking, perhaps a possible foreshadowing of the kind of loss of paradise
this novel will eventually depict. In any case, by the end of the novel, the present
passage will seem highly ironic.