The first King Air Model 90 serial # LJ-1 rolled off the Beech assembly line Oct 30, 1963. It was certified in March of 64.
That particular aircraft is still flying.
I got the info from the March 2004 Air& Space magazine.
I fly a C90A, One notable difference between the B90 and a
C 90A are engine intakes the C90As use the pitot style intake heated by exhaust gases while the B90 is similar to the 100 intakes and are electrically heated (I think).