Now - Rather, “and.” The conjunction here probably has the same connecting force that it has at the opening of Joshua, Judges, 1 Samuel, etc…

Now king David.—“Now” is the simple illative conjunction “and,” found at the beginning of all the historical books (Exodus, Number…

Now King David was old, [and] stricken in years
Was seventy years of age; for he was thirty years of age when he beg…

We have David sinking under infirmities. He was chastised for his recent sins, and felt the effects of his former toils and hardships.