I used to work in the Vancouver film industry.  I remember an interview with some of the Stargate people where they laughed at the fact that most of the CG guys working on the shows final years (SG Atlantis) were in diapers when SG1 started.  As soon as the novelty wore off and they wanted pay, everyone left.  Anyone who thinks actresses age quickly in Hollywood, look at the teenagers who work in CG.