It was announced late today that Sally Field will play Mary Todd Lincoln, the wife of the nation’s 16th President, in Steven Spielberg‘s Lincoln, which begins filming next fall for release in late ’12. The Oscar-winning Field obviously resembles the former First Lady and will, I’m sure, play her with snap and spunk to spare. But if I’d been casting, I’d have given the role to Marcia Gay Harden.

No offense but I think Field is too old to play the role and that Harden would be exactly the right age for it, and that her appearance wouldn’t stir audiences to talk and whisper the way Field will, I fear.

I realize, of course, that photos of Mary Todd Lincoln have always shown an anxious and clenched and worn-down appearance, and that one result was that she looked older than her years. But Lincoln, I’ve learned, will focus on the years 1863 to ’65, when Mary was 45 and 46 years old. Field is 64 and will be nudging 65 when filming begins six months hence.

In actuality Mary Todd Lincoln, born in 1818, was nine years younger than her husband Abraham, who was born in 1809. Daniel Day Lewis, who will play President Lincoln, is 53 now and will be 54 when filming begins — ten years younger than Field. (Lincoln was 56 when he was assassinated in April 1865.) So in Spielberg’s version Mrs. Lincoln will not only be played by a woman 20 years older than the real Mary Todd, but nearly ten years older than the real-life Lincoln.

Harden, an indisputably brilliant actress, is 50 — a little more than two years younger than Lewis. She would be 51 when filming begins. She would be about five or six years older than Mrs. Lincoln was at the time, but no biggie — makeup and lighting would fix any problems. But age gaps of 10 or 20 years are another matter. I’m not saying Field’s age will be a significant issue, but her appearance will, I suspect, have to be worked around to some extent.