Perhaps one might get a better perspective to consider how long it would take a complete newbie to the English language to read Shakespeare's plays competently, or Chaucer?
Here are the opening lines of Chaucer's "The Canterbury Tales" -- "When that April with his showers soote its showers sweet, The drought of March hath piercèd to the root, And bathèd every vein in such liquor rootlet / liquid Of which virtúe engendered is the flower"
And Shakespeare's well known verse from "Troilus and Cressida":-
"One touch of nature makes the whole world kin:
That all with one consent praise new-born gauds
Though they are made and moulded of things past,
And give to dust that is a little gilt
More laud than gilt o’er-dusted"
Of course we must also factor in such intangible qualities like determination, interest, innate abilities, the learning environment, and, dare I say it, intelligence?
Many of the contributors here have studied and grown up with the Chinese language all their lives, and how many could read and understand those Text you presented?
Having said all that, I am not suggesting you can't do it, but how long? As the saying goes, we'll know when you get there. There are, as Donald Rumsfeld said:-
"As we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don’t know we don’t know"
Also search around the various questions asked on this Forum. These concern mostly modern Chinese language usage. Not exceptionally difficult or "classical" Even then we could see basic comprehension problems by people who already have some encounter with the language.
Perhaps an in-depth understanding of Chinese culture itself assists in grasping the finer points.