The age of the airframes is less relevant here than their specific capability.
My overall point is that all aircraft prior to domestic PRC 4th gen planes (i.e.: J-10A, J-11B era), inclusive of J-7, J-8, JH-7, and Russian built or subsystem Flankers (27SK, J-11A, Su-30s) are going to be targets for retirement and replacement by domestic 4.5th and increasingly 5th gens, and the role of those older aircraft is as much for simple air policing as they are for keeping the relevant units active and running to enable a more graceful/easy re-equipping with modern aircraft.
How useful/relevant do you think is the JH-7 compared to J-11B when it comes to anti-ship and land-attack missile truck role?
How long do you think they will keep the JH-7 if they have unique capabilities that other planes do not have.