This:
And
It does seem like a bit of a waste, considering how older fighter pilots would have more experiences than younger ones.
However, given how youngsters today typically have better knowledge and understanding at using all sorts of modern gadgets (e.g. smartphones and computers) than their parents - The same can be said with all the new technologies, skillsets and methods of conducting aerial warfare that are typically better mastered by younger pilots compared to older pilots. All the new kinds of skills and knowledge that are always evolving and upgrading are much easier to be picked up by the youngsters compared to the elders too.
It is indeed true that we are gradually living in a new world where "higher age = better" no longer applies as much as before.
In the meantime, while retaining the older fighter pilots to keep flying older fighter types until retirement is one way to go with - I'd prefer more if these older pilots can be relegated/retrained to fly airlifters, tankers and special mission aircrafts. Flying these "heavies" frequently entails longer flight hours, but less physically and mentally taxing to the (aging) bodies of military pilots compared to flying highly-agile fighters. This should guarantee that while older pilots can continue serving with the PLAAF until retirement, the fighter fleets of the PLAAF can be upgraded and expanded faster and across-the-board as well.