n. Discrimination based on a person's gender and age, particularly discrimination against older women.
It is ironic that women broadcasters have coined the term sageism , with its suggestion of wisdom, to describe the toxic combination of sexism and ageism that many claim forces them off the television screen after they reach 50.
—Jennifer Cunningham, “Glad to be going grey? Only if you happen to be male,” The Herald, September 20, 2012
Yesterday, concern over the disparity flared up, with a series of high-profile women speaking out against "sageism" — what they see as a toxic combination of sexism and ageism — by which competent and popular female broadcasters are shunted into the sidelines.
—Emily Dugan, “You won't see women going grey in front of the cameras,” The Independent on Sunday, April 12, 2009
1997 (earliest)
Interesting, isn't it, that The Times reports that 18 feature films produced in 1996 starred male actors over age 65. Wanna guess how many women over 65 played the lead role in a movie? One - 69-year-old Jeanne Moreau.

I wonder if there's a word that combines "sexism" and "ageism"? "Sageism," perhaps.
—Sue O'Brien, “People of a certain age,” The Denver Post, March 16, 1997
Another sense of this term has almost the opposite meaning: to appreciate the wisdom that comes with old age. See, for example, A Call to Action: From Ageism to Sageism.