Yes, the average fleet age is held down a little because of the QC's, but they're unique, and you're right pug, it is something to keep going during the quiet winter period. Thums up to dreamair's comment further up ^.
In response to mockingjay, Jet2 and Jet2holidays run in unison, and on the same booking system. Jet2 don't sell seats to Jet2holidays, but as they run on the exact same booking system, it means that Flight Only and Holiday pax figures can appear rather different to other airlines.
The difference between LS and EZY is that EZY are now a European wide operation, which means they operate flights from foreign airports to foreign airports, just like FR. Jet2's business model is somewhat different, in the way that they only fly UK-DESTINATION-UK, and not sectors within Europe. Because they only from the UK, they really only serve passengers going on holiday, or maybe a few from Spain wanting to come to the UK. EZY serve a whole European market, and because their business model, like FR, is purely LCC, they tend to earn that bit more.