Research confirms what we already knew.
In nine out of 12 tests the average age at which the top performance was
achieved was 22.
The first age at which performance was significantly lower than the peak
scores was 27 – for three tests of reasoning, speed of thought and spatial
visualisation. Memory was shown to decline from the average age of 37. In the
other tests, poorer results were shown by the age of 42.
I had already decided to stop reading so many new books and instead re-read good books I've already read. Sounds like reinforcing that old information might be a good idea before it slips away.