The big caveat to that, being that you need to make sure whatever proxy marker you're looking at remains correlated even in the treatment setting. It doesn't s

The big caveat to that, being that you need to make sure whatever proxy marker you're looking at remains correlated even in the treatment setting. It doesn't seem like there would be a good way to do that without running the longterm studies you're trying to avoid. We may be better off basing research on more directly detrimental aspects of aging. e.g. using mobility and mental acuity as end points instead of a biomarker. That way even if a "rejuvenation" therapy which is successful in the short term doesn't extend life, it still provides some benefit.