Generally speaking, most actors, actresses, and directors either get that once-in-a-lifetime Academy Award nomination, or, if they're lucky, a couple or a handful of nods within a period of two to fifteen years. There are a number of exceptions to that rule, of course, but in the Academy Awards' 83-year history very few performers and directors – 28 of them, to be exact – have received Oscar nominations after a gap of 20 years or more in their respective categories, i.e., actors/acting categories; directors/Best Direction category.
On the next page (please see link below) you'll find a complete list of Oscar's major “comebacks” – actors and/or directors who had to wait two decades or longer in-between nominations. Among those are record-holder Henry Fonda (41 years), John Huston, Julie Christie, Roman Polanski, Mickey Rooney, Alan Arkin, Lynn Redgrave, and Jeff Bridges.
Below is a list of 28 actors and directors who had to wait 20 years or more for the next Academy Award nomination in their respective categories, i.e., actors/acting categories; directors/Best Direction category. That's why Henry Fonda is listed first with a 41-year gap between nominations, even though he was shortlisted for the 1957 Academy Awards as one of the producers of Best Picture nominee 12 Angry Men.
Also, unless otherwise noted, the acting nominations are for leading roles. Years in bold represent Oscar victories.
41 years between nominations
Henry Fonda (1940, The Grapes of Wrath; 1981, On Golden Pond)
Helen Hayes (1931-32, The Sin of Madelon Claudet; 1970, supporting, Airport)
Jack Palance (1953, supporting, Shane; 1991, supporting, City Slickers)
Alan Arkin (1968, The Heart Is a Lonely Hunter; 2006, supporting, Little Miss Sunshine)
Ralph Richardson (1949, supporting, The Heiress; 1984, supporting, Greystoke: The Legend of Tarzan, Lord of the Apes)
John Huston (director) (1952, Moulin Rouge; 1985, Prizzi's Honor)
Lynn Redgrave (1966, Georgy Girl [right, with Alan Bates]; 1998, supporting, Gods and Monsters)
Paul Scofield (1966, A Man for All Seasons; 1994, supporting, Quiz Show)
Richard Harris (1963, This Sporting Life; 1990, The Field)
James Whitmore (1949, supporting, Battleground; 1975, Give'em Hell, Harry!)
Julie Christie (1971, McCabe & Mrs. Miller; 1997, Afterglow)
Christopher Walken (1978, supporting, The Deer Hunter; 2002, supporting, Catch Me If You Can)
Peter O'Toole (1982, My Favorite Year; 2006, Venus)
Fay Bainter* (1938, White Banners, and 1938, supporting, Jezebel; 1961, supporting, The Children's Hour)
William Holden (1953, Stalag 17; 1976, Network)
Mickey Rooney (1956, supporting, The Bold and the Brave; 1979, supporting, The Black Stallion)
Charles Laughton (1935, Mutiny on the Bounty; 1957, Witness for the Prosecution)
Roman Polanski (director) (1980, Tess; 2002, The Pianist)
Gladys Cooper (1943, supporting, The Song of Bernadette; 1964, supporting, My Fair Lady)
Richard Farnsworth (1978, supporting, Comes a Horseman; 1999, The Straight Story)
Wendy Hiller (1938, Pygmalion; 1958, supporting, Separate Tables)
Joseph L. Mankiewicz (director) (1952, 5 Fingers; 1972, Sleuth)
Ellen Burstyn (1980, Resurrection; 2000, Requiem for a Dream)
* Fay Bainter was nominated as both leading and supporting actress in 1938. She won in the latter category.