Yes, the 14 year record goes to Randy Johnson...
--Time between 1st and last no hitters--
Johnson 6/2/90 - 5/18/04 = 14 years, 15 days
Ryan 5/15/73 - 5/1/91 = 13 years, 351 days
...but Ryan was 44 when he did this.
He never pitched a perfect game tho.
What an accomplishment!
Um..its 18 not 13 years between 1973 and 1991.