geezer glut
n. The large number of seniors that will result as the baby boom generation ages.
Federal Reserve Chairman Alan Greenspan has called it a potential time bomb, a period of global economic stagnation triggered by falling fertility rates and increasing life expectancies.

As the populations of the world's industrial nations grow older, the fallout could be devastating, leading to chronic labor shortages, higher taxes, shrinking numbers of consumers and governments in default. …

The approaching "geezer glut," as one national magazine coined it, will impact everything from personal pension plans and retail trends to hiring practices and immigration.
—Dave Anderton, “Globe turning gray,” Deseret News (Salt Lake City, Utah), April 20, 2003
1997 (earliest)
Now we boomers are over or nearing 50. Though we're still more numerous than any other generation, it's getting silly to speak of us as the baby boom; we're destined to be the "geezer glut" — the most tiresome generation in history.
—Joseph Sobran, “Baby boomers are becoming Geezer Glut,” Las Vegas Review-Journal, June 01, 1997
Back in 1946, when the baby boom began (in the U.S., anyway), there were 11 million people aged 65 or older. By the time the first boomers turn 65 in 2011, there will be 40 million people who are 65-plus, and that number is expected to leap to 70 million by the time the last of the boomers turn 65 in 2029. That's a lot of people having senior moments, hence this notion of a geezer glut, the logical chronological conclusion of the baby boom. (The mildly derisive term geezer (1885) makes this phrase unlikely to be used by boomers themselves, although one suspects the members of Generations X and Y might take a shine to it.)