WHEN Bert Parks croons his trademark beauty pageant song, ``There She Is,'' to 26 former Miss Americas on Saturday evening, his appearance will mark a triumph of sorts for the 75-year-old performer. Exactly 10 years ago he was fired as host of the Miss America pageant - a position he had held for 25 years - on the grounds that he was ``too old.'' Mr. Parks will appear in only one segment of the two-hour show, and co-host Gary Collins will retain the honor of singing to this year's winner. But Parks's return should help to soothe the ``residual resentment'' he admits he has harbored since his ouster. It should also serve as a highly visible reminder that ``too old'' is a subjective term - one increasingly at odds with new realities of longevity and vitality.
Parks, of course, is only the most casual example of never-say-quit ambition. Akira Kurosawa, an 80-year-old Japanese filmmaker, is receiving enthusiastic reviews for his latest film, ``Dreams,'' which opened in the United States two weeks ago. Not content to rest on his laurels, Mr. Kurosawa has already begun work on another film.
In the theater, Jessica Tandy, also 80, created the role of a lifetime with her performance in ``Driving Miss Daisy.'' And John Gielgud, at 86, shows no signs of letting the curtain fall.
Then there are the late-life achievers in the world of literature. Many readers and critics still consider 86-year-old Graham Greene to be the best living English novelist. V.S. Pritchett, now 90, can be defended as the best living critic. Novelist Anthony Powell is 85 and still writing. And one of the current darlings of the British book industry, Mary Wesley, published the first of her six novels at the age of 71.
Not that mature creativity represents a contemporary phenomenon. Sophocles was working on ``Electra'' at 75. Michelangelo was completing the walls of the Pauline Chapel at the same age. Haydn was around 70 when he wrote the oratorio ``The Seasons.'' Goethe wrote the second part of ``Faust'' at 82. Chagall, Matisse, and Picasso were all painting well into their 80s. And at 75, Hokusai, the Japanese wood-block master, described himself as ``the old man mad about drawing.''
But it will take more than the achievements of scattered octogenarians and septuagenarians to bring about widespread changes in attitudes about age. As one solution, Britain's Lord Young envisions an ``ageless society'' in which everyone's date of birth would be private information, erased from employment records and government computers.
``As long as everyone's vital statistics are kept by the state in a vast storehouse where all of us are docketed and to which the state always has instant access, the state will always be able to haul us before the court of enumeration, to declare that we are too young for this or too old for that,'' the Times of London has quoted Lord Young as saying.
Arguing that there is a ``widening gap'' between biological aging and ``social aging'' - the roles society dictates for people at different ages - Lord Young makes a persuasive case for radical social reforms in which education, work, and leisure would be more equally spread throughout life. He also predicts that the 21st century will be marked by ``a far-reaching liberation from ageism.''
In James Thurber's charming parable, ``The 13 Clocks,'' to be published next week by Donald I. Fine after years out of print, the humorist describes a gloomy castle on a lonely hill where all the clocks have been frozen for seven years - the work of a cold-hearted Duke. As travelers pass by the castle they remark sadly that ``Time lies frozen there. It's always Then. It's never Now.'' The cold Duke, Thurber explains, ``was afraid of Now, for Now has warmth and urgency, and Then is dead and buried.''
Beyond talent, perhaps what sets all late-life achievers and activists apart is a sense of Now, with all its warmth and urgency. ``Now'' is a country of no numbers - as free from a bureau of vital statistics as Lord Young's dream. When this concept of ``Now'' is celebrated in a pageant, complete with theme song, the Age of Agelessness will have come - and about time!