Steve Lucky and the Rhumba Bums were busy "shooby-doo-wop-bopping" on stage. Meanwhile, a woman with a black halter dress, a chic A-line haircut and flashy white sunglasses jitterbugged with the man in the suit. The couple was eye-catching. They were not only good dancers, but they were an older couple. This Memorial Day weekend marks Sacramento's 36th Jazz Jubilee. If you have never been to the Sacramento Jazz Jubilee, or JazzFest (they are referred to interchangeably), a consistent observation has been the strong presence of an "older" crowd. This can be attributed to the festival's traditional Dixieland appeal, an appeal that some patrons said is beginning to fizzle out. Volunteer Joh