Flouresent tubes inkitchen take too long to come on, it has been 6 years since fixture installation,

They just aren't worth trying to troubleshoot and fix. These days, LED lights are so efficient that they are fast replacing the 3 other kinds. The fixtures themselves, and the wiring, are the same as for incadescent (regular old bulb) but take an LED bulb.

Are the ends of the blubs dark/black? If they are then replace the blurbs.

If the bulbs appear to be fine then it may be the ballasts or if the light is old enough it may be the starters.