A lot of talk on here is behavioural coping mechanisms, and not much talk of actually repairing the damage aging has caused to the brain.
One of the main problems with learning and keeping mentally agile is the accumulation of lipofuscin on the dendrites in the brain. Lipofuscin is a pigment; age spots are made of it, and it accumulates in the brain and liver. It's made of broken pieces of cell membranes and other crap. And it's plaquing up our brains! The brushy tips of the dendrites are where the mental connections are made, and there's less available surface area when lipofuscin is mucking everything up. So take centrophenoxine.
Rat studies show a significant reduction of lipofuscin (about 40% in middle-aged rats) after a month. This effect is potentiated by piracetam and similar drugs (all of which can be had online nowadays).
Piracetam (and the others that came after) cause the brain to use more glucose and choline, which get turned into acetylcholine, a neurotransmitter. These drugs were originally developed to repair damage caused by alcoholism and hypoxia. Good stuff, Maynard.
Also the previously suggested exercise, eating less/no red meat, meditation etc are all important as part of the program. AND QUIT WATCHING TELEVISION.