The USN has (post USS Midway) managed to get around 40-50 years out of their carriers, largely because they were built sufficiently big in the first place.
The RN experience is different, principally because our ships were either war-designed / built and therefore subject to all sorts of constraints that impacted on ability to operate aircraft, or were size limited without the intention of actually being a true aircraft carrier (CVS).
There are a number of things that point towards being able to achieve a longer life with QEC, principally due to the reduced manning levels and high-spec accommodation being applied, which takes accommodation standard increases (a real life-ender) out of the picture. This can be a two-edged sword however, when it comes to supporting ship systems which have a finite component life. Hopefully open-architecture being applied will mitigate this to some degree. The ships are also being designed with adequate margins (stability, structure and power etc) combined with a realistic environmental spec which will also help. All the above (combined with a consistent failure to allow for defence inflation in budgets, hence force structure cuts which also apply to Army & RAF) have led to RN selling on ships early.
Hopefully, the sort of capability-changing refits seen in the past will be reduced in favour of keeping the material state good with capability updates / system obsolescence updates as required.
Famous last words etc........