Daniel Hamermesh argues that innovation in economics is slowing, and that allows older economists to stay in the game longer than in the past:
Ageing and productivity: Economists and others, by Daniel S. Hamermesh, Vox EU: Is economics still a young person’s game? If not, what is changing? This column argues that although top-level economic research in the 1990s was very much a young person’s game, the last 15 years has been kinder to older economists. More and more economists over 50 are being published in the top journals. Why? Because technological change in economic research is slowing, giving young researchers less competitive edge. ...
There's an alternative explanation. Older economists have more power over journals and other key research outlets than they used to, and they have kept the topics they work on alive much longer than in the past.
As for the thesis about technological change, it may be true about micro, though even there I'm not sure -- Varian does differ from Mas-Colell -- but what students in macro learn today is very different, both in technique and content, from what they learned 50 years ago. Same for some aspects of econometrics, e.g. the rise of the Bayesians. But if you take a shorter horizon in macro, since the rise of DSGE as a technique, and consider the forces for change that ought to exist in macro presently, it's harder to disagree with the stagnation thesis Hammermesh puts forward (which is mainly over the last 15 years). I think it's the hold that some of the "older" macroeconomists still have over the journals, NBER meetings, and the like -- that allows them to steer the theoretical agenda. But it's mostly just an hypothesis, I don't really have any hard evidence to back it up and I'm not all that confident it's correct. Maybe it's just that nothing better has come along.
In any case, here's a hint he's mostly thinking about micro:
In no way should the implied slowdown in methodological advance be viewed as negative for the profession as a whole. For the role of economics in society, the question is whether the profession is keeping up with the problems of an evolving complex society, not how it solves them. While one might despair of our progress in understanding issues and offering solutions for macroeconomic difficulties, the remarkable advances in the application of microeconomic ideas to real-world problems should be reassuring.
The "implied slowdown in methodological advance" might be okay for microeconomists, and for the "profession as a whole" if micro carries the most weight, but innovation -- perhaps aided by a change in the power structure within the profession -- is surely needed in macro.