senior moment
n. A momentary lapse in memory, particularly one experienced by a senior citizen.
Examples
2002
As baby boomers age, memory loss looms large in America. This being the land of marketing opportunity, that means we'll be seeing more and more things designed to help. We've already produced a term for the problem: "Senior moment" was named Word of the Year (even though it's two words) by Webster's New World College Dictionary a couple of years back (who can remember when, exactly?).

There is a natural decline in short-term memory as we age, which can be annoying. Among the products that step in when memory falters: Post-it notes, those "pill-minder" boxes with mini-compartments for each day's medications, e-mail and voice mail for self-reminding messages, and keychains that let you make your car chirp to you when you forget exactly where you parked it.
—Alison apRoberts, “Keeping boomers sharp,” Sacramento Bee, December 24, 2002
1996
Hospital officials knew of Queens' large elderly population, but they were still surprised when 200 seniors packed the Parker Jewish Geriatric Institute auditorium for a workshop on memory loss.

The turnout Wednesday afternoon was nearly four times that at any other health care workshop held at the New Hyde Park facility, according to officials at the institute. Officials estimate some 400,000 senior citizens live in Queens. "Just like the physical signs of aging, such as gray hair and stiff joints, memory loss is a cognitive sign, and that concerns us all," said Dr. Gisele Wolf-Klein, the guest speaker. . . .

Cecile Herman of Bayside said she worries about her memory loss. "Sometimes I can't think of the words when I'm talking. The idea is in my head, but I'm choking on the words." . . .

Evelyn Weinstein, who works with 35 nursing homes in Nassau County, came to the conference for herself and her patients. "I really want to learn what I can for our people," she said. "And I've had a few 'senior moments' myself."
—Lilo Stainton, “Impressive turnout for workshop on memory,” Daily News (New York), November 15, 1996
1996 (earliest)
Please ignore this person. He is obviously suffering from a senior moment (or a brain fart, you choose).
—Joan Ellis, “Probably the most stupid question to ask in this group,” rec.food.cooking, May 03, 1996
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