PN
Looking at OldGrubbers post too, it is patently obvious that someone had to be telling porkies over a 50-year life.
Not so. If you design and plan for a 50 year life (margins etc) then it will be able to do so. CVF has a stonking growth margin in for stability - strength usually less of a problem in a deep multi-deck ship, plus system margins as well. The problem is where you don't do that and try to run ships beyond their design lives (eg CVS 25-20 yr design life as a helicopter carrier, not an aircraft carrier).
XR219 - Leanders died because they were manpower intensive (250 crew) and developed stability problems as they got old. Puma airframes (and BUFFS for that matter) can be stripped down and blasted to bare in depth maintenance relatively easily (you don't have a couple of hundred compartments in an airframe - except maybe XH558!)
LO - The days of massive aircraft weight (and size) increases are hopefully long gone - topped out in ~1972 with the F14. In terms of impact - it depends on the size of ship relative to CAG. Lightship of a CVN is ~ 60000 te and assuming a 85-ship CAG with an average weight of 25 te, the aircraft payload works out at 3.5% - can't see the frames getting much heavier. On a CVS, the equivalent is closer to 2%. Not really going to make a huge difference.