Clued by "I couldn't even remember the month when I started" you're
supposed to figure out that each person's birthmonth is important.
Listed in order of birthday are the 15 people:
Faye Dunaway (1/14)
Oliver Hardy (1/18)
Oprah Winfrey (1/29)
Louis Rukeyser (1/30)
Oscar De La Hoya (2/4)
Hugh Hefner (4/9)
Golda Meir (5/3)
Molly Picon (6/1)
Kevin Spacy (7/26)
Isaac Hayes (8/20)
Gwyneth Paltrow (9/28)
Chris Kirkpatrick (10/17)
Winston Churchill (11/30)
Barbara Billingsley (12/22)
Johnny Gruelle (12/24)
Taking the Nth letter in each name, where N is the month, you get:
FOOLSHAPPYAPRIL
Or if you start the year in April, you get HAPPYAPRILFOOLS (the answer)