Old minds are like old horses; you must exercise them if you wish to keep them in working order.

The quotation is attributed to John Adams in his last illness.

This is how I exercise my mind.

John Adams. I have a vague idea that he was an American president.Vague ideas are no good to me. I have to find out the FACTS.

John Adams (October 30th, 1735 – July 4th, 1826) was the second President of the United States (1797–1801).

 ...and he had an interesting hairstyle, which reminds me of Moses parting the Red Sea. But I mustn't get distracted by that because I'm already distracted by the idea that another John Adams was a Georgian architect, famous for his fireplaces.

Excuse me a moment.

Nope. That was Robert Adam (3rd July, 1728 – 3rd March, 1792) He hasn't got an interesting hairstyle so I won't bother you with a picture of him but instead...a fireplace:

See, now my mind is exercised, as well as my horses.

Is my mind in good working order? Not by most people's standards maybe - but perfectly acceptable for muddle-headed me