I think you are on to something, Jim. I too feel that repeated going to altitude on a regular basis helps even if you go back down to sea level inbetween. It is almost like you are developing body memory. Getting better at altitude as you get older may be just that you have a lifetime of going to hights on a regular basis. Or it could simply be that we old farts are not fast enough anymore to over-do at altitude!

I have been told by a medical person that there is a break-over point. If you over-do it and get seriously out of breath, that sets up a reaction that contributes to altitude sickness. If I go up to 12,000 feet from sea level and get out of breath, I do not seem to be able to recover and it is all down hill (or upchuck) from that point on. Slow and easy rythmic breathing really helps me until my body truely aclimitizes.