>General Relativity derived elsewhere would have taken decades at least

Is this based on the quality of evidence you used when you claimed people over 40 don't do much science? That turned out to be wildly incorrect.

What do you base the "decades" claim on? There was no new math needing invented, no new empirical evidence needed, no new physics needed, and many people were close at the time, and certainly more and more physicists were heading down the same paths.

BTW, Einstein's most cited paper, by far, is from 1935, written when he was 56. I suspect that's some evidence he did good work after general relativity.