And at an age when most of his colleagues are, in his words, "crocked up," the psychoanalyst has just published a book.
Not one for understatement, Appel describes his slim volume, Who's In Charge? Autonomy and Mental Disorder, as nothing short of a "how-to book for staying sane."
It presents his theory, gleaned from years of sitting in the analyst's chair, that an individual's autonomy and independence are critical to his sanity, that overly controlled people feel helpless and may eventually become mentally ill.
Explaining why he believes the book would be helpful to just about anyone, he says, as if confiding, "I don't know how many people realize that they can really lose it."
Appel - on this day wearing Nike running shoes that glow chartreuse and fuchsia under the light, and a light-blue suit jacket with a red handkerchief tucked in the breast pocket - is not afraid of being a tad irreverent.
The former senior attending psychiatrist at Pennsylvania Hospital refers to himself and his colleagues as "shrinks" and to various unnamed patients as "crazy."
The Harvard alumnus has a copy of pop psychologist Laura Schlessinger's latest book on his coffee table. He jokes that he's happy to at least be in semiretirement because "it cuts down on my malpractice insurance."
But when Appel puts the jokes aside, it becomes clear that he has devoted his life to making psychotic people well.
Perhaps one of his grimmest assignments was also one of his first. During World War II, he was working for the Surgeon General's Office, studying a soldier's "breaking point," the moment when he might lose his mind if forced to stay on the front line any longer. Appel said he was instrumental in instituting a 180-day time limit on active combat.
"Before that, some soldiers would do anything to be honorably discharged," he said.
After the war, he returned to Pennsylvania Hospital, became an assistant professor at the University of Pennsylvania School of Medicine, and opened a practice.
Since then, he says, his profession has changed enormously. While once it was taboo to see a psychiatrist, today "it's even fashionable," he says. And while psychiatrists used to employ what he calls "talk therapy" to treat patients, treating them with medication has become increasingly popular.
"I almost think it's malpractice," he says of drug therapy. "You may get over your depression, but you didn't get to the source of the depression."
Appel's colleagues credit him with being an independent thinker.
"He has his own ideas, and he is a thoughtful person," says Philip J. Escoll, a Philadelphia psychiatrist who trained under Appel. "He's not one to try to placate someone. . . . It's a good quality he has."
Appel sees patients for about 12 hours a week at the home he shares with his wife, Marian. He jogs up and down his street in the morning, reads several newspapers every day, and corresponds by e-mail. Lately, he says, he has been thinking of designing his own Web site.
But one thing hasn't changed: Treating people is still a rush.
"One of the most fascinating things in the world is getting to know your patients," he says.
Plus, now he has an ulterior motive: "It's so thrilling for me to see the theory in my book continually realized."
He says the majority of his patients, even today, suffer from having let themselves be controlled by others - parents, spouse, coworkers.
So as not to let that happen to him, Appel says, he practices autonomy even in small ways. Announcing a demonstration, he sits down at a baby grand piano in his living room and begins to play. The sound is melodious, if a little halting.
After about a minute, he stops and gets up.
"You see," he says, "I was making it up as I went along, improvising. That's freedom, that's autonomy for you."
Erin Carroll's e-mail address is firstname.lastname@example.org