I saw a documentary on Long March rocket development that talked about this. There was a period in the late 80s where the economic reform was under way and while previously the government paid for all the costs of aerospace program in China, they were told instead to "fend for themselves" in the international launch market. Funding was so low that rocket factories had to build refrigerators just to survive. Naturally pay was also really bad and lots of people left the industry and few new blood wanted to join, so only the really dedicated remained.
Long March rockets went onto the international launch market in October 1985, then something surreal happened in 1986. In one single year the Challenger Disaster first happened in January, then a Titan III blew up in April 8 seconds after launch, then a Atlas III blew up in May followed shortly by an Ariane 2 in the same month.
With everyone's launch vehicles all grounded at the same time there was suddenly a vacuum in the satellite launch business and China was all too happy to pick up the slack.
China started picking up business with Long March 3 but they very quickly realised that satellite will shortly outgrow the puny 1.5 ton to GSO that Long March 3 offered. So someone came up with Long March 2E, the first Long March with boosters.
But the government at the time said they won't foot the R&D cost until a customer could be found for Long March 2E, since there's no domestic need yet for a launch vehicle in this class. So MAI did a crazy thing were they went looking for customer with only the rough blue prints in their hand and a promise that they would be on time with the rocket. Fortunately on this occasion Pakistan and Australia came through for China. The negotiation went for so long though that after the handshake there was only 18 month left before the launch deadline, but MAI made it and first Long March 2E was launched before the deadline successfully with Badr-A and an Optus B mass simulator. After this funding gradually started to loosen up and the space program recovered overtime.
So the lack of middle aged people in China's space program actually has a lot to do with this dry period.