John Paul Stevens had served 341/2 years on the U.S. Supreme Court when he retired in June of last year. That made him the third longest-serving justice in the nation’s history, and his age at the time — 90 years and two months — made him the second-oldest to have sat on the court, just behind Oliver Wendell Holmes. So has Stevens been relaxing? Not much, it turns out. He’s just come out with a new book, “Five Chiefs,” a compendium of memories of each chief justice he served with, from Fred Vinson through John Roberts, and a treatise on his beliefs that each justice, not just the chief, influences and molds the highest court in the land. “The Chief Justice of the United States has often been described as the ‘first among equals,’ ” Stevens writes. “He is ‘equal’ because, like each of his eight colleagues, he has only one vote. It takes a majority of equally powerful votes to support a decision on the merits in any case before the Court.” Stevens, a great-grandfather who splits his time between Washington and Florida, recently discussed with The Washington Post his post-court life, his recent reading list and how aging helps an intellectually driven life and vice versa.

Laura Hambleton

I hear you once said 70 was the optimal age to retire.

I am not sure I said that. In my second or third year on the court, I asked one of my law clerks to do a study at what age most Supreme Court justices retired. And I think he told me somewhere around 70. And I thought that might be the appropriate age to retire. Then time went on, and I didn’t retire at 70.

How did you know it was time to retire at 90?

Thought it was time.

Did age bring you more wisdom to your job?

Well, I don’t think it brought me more wisdom. It brought me more knowledge. I learned a great deal in the years after I reached 70. Working at the court is a learning process.

There are constantly new issues coming up or issues like the issues you have studied over the years, so your prior experience helps you with problems you confront. That’s the same as in almost any profession: The more experience you have, the better able you are to find the right answer to the problem.

What should you do to stay intellectually vigorous?

To continue to work on problems that require thought and analysis helps you keep up your ability to do that sort of thing.

You are one of three of the longest-serving Supreme Court justices. Who are the other two?

Justice [William] Douglas, whom I succeeded, is by far the longest, and the second is Justice [Stephen] Field, who I guess I would have exceeded if I stayed around another week or two. I didn’t realize it at the time.

You might have stayed on?

I retired at the end of the term a year ago. If I had retired two or three weeks later . . . I would have exceeded him.

How do you stack up against these other two justices?

That’s up to some third party to say. Not for me. I did my best, but whether it was good enough is for someone else to decide. Justice Douglas was a brilliant, brilliant man, and so was Justice Fields, but I understand in the last several months of his career, he was not able to do his work. People say he should have retired seven or eight months earlier.

What about you?

Some people say I should have retired 25 years earlier.

Tell me about your book. Has it been in the works a long time?

No, I wrote it in the year since I retired. It took several months before it was done. I wouldn’t say I worked full time on it, but I spent a good deal of time on it. I enjoyed doing it. I took a subject, and started writing about the five chiefs. I took a draft and showed my law clerk, my wife and agent, and they made suggestions. I have written articles before. This was a book, so it took more time to complete. Just like working on some opinions, I would write one chapter, stop and think about what comes next.

Tell me about your retirement. Do you prefer this time in life?

What’s my choice? I definitely made the right decision to retire. I am still keeping busy. I’ve written books, as you may know, and I am giving talks from time to time. I am watching movies once in a while. I’m watching the Redskins. Life is much more like when I was an active judge than I expected.

Then it isn’t a retirement?

Well, it is because I am no longer an active justice; I don’t have the very heavy responsibilities that they do. But I continue to engage in work I enjoy. One of the nice things about retirement is you’re not frozen into one schedule every day. I play a little tennis, some days we go to movies, some days we play a little bridge. Some days I work on things I am writing about.

[In a follow-up e-mail about his recent movie and book choices, Stevens wrote: “Recent movie: Moneyball. Recent books: Destiny of the Republic – A Tale of Madness, Medicine, and the Murder of a President, by Candice Millard; Contested Will, by James Shapiro; Unbroken, by Laura Hillenbrand.”]

What can we expect from you in another year?

A few more talks, I suppose. I’d like to say a lower golf score, but that would be unrealistic.