KJV is olde English.

While the language of the KJV seems "olde" it is actually considered toward the beginning of the modern version of English. Olde English would be Beowulf. Here are the opening lines to the poem:

Hwæt. We Gardena in geardagum,
þeodcyninga, þrym gefrunon,
hu ða æþelingas ellen fremedon.

Middle English would be more Chaucer where we start to figure out some of the words. Here are the opening lines to his Canterbury Tales:

Whan that Aprille with his shoures soote,
The droghte of March hath perced to the roote,
And bathed every veyne in swich licóur
Of which vertú engendred is the flour;

Much more modern sounding, but still not entirely decipherable.

The opening lines to Genesis are:

In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.

We can read and understand every word here. Now, of course, the language has evolved in 400 years, but it is nowhere close to being as unreadable as Beowulf.

Roughly speaking, the Old English historical period is 500 to 1150 (or about 100 years after the Conquest); Middle English from 1150-1500 (first years still evolving from Old to Middle); Modern English from 1500 to present.

Pete