How do these swimmers swim so fast?

Looking at one-hour results, and just finishing New England Masters SCY Championships at Harvard, how is it that older swimmers are getting faster and faster, and pretty much everyone is getting faster and faster compared to a few years ago when there seemed to be more mortal swimmers? What are older (45+ women; at this point 65+ men) swimmers doing that keeps them at such elite levels? Weights? Extensive training? How much of both? How do they have jobs and families and train? The field of fast swimmers is getting deeper and deeper. Anyone have idea as to why? I want to know the secrets. Are the people who race now self-selecting more and more as elite swimmers? Has everyone swum all their lives? I know to swim hard you have to train hard, but I am baffled by sudden increase in amazing fast times and so many records getting broken.