Topaz, you really have nothing to worry about. Those jets are getting on a bit but there are aircraft flying with the US majors that are every bit as old if not older. Jet2 are relatively successful and like all airlines they have to do things by the book, so regulated is the industry on that side of things. When an airline strays away from this then you will get to hear about it pretty quick.
I know Jet2 have their fair share of aircraft going tech by the sounds of things but I would happily board one of their flights with complete confidence that it was fit to fly. From a crew member who works for a larger competitor using very new aircraft, your worries are unfounded mate.
The engine fans often blow in breezy conditions.