Few artists find themselves in their studios at age 90, exploring questions they posed in their youth. But Ellsworth Kelly, the abstract artist who began his career in the 1950s, continues to hop on his ladder to build new works that blur the boundary between painting and sculpture.

The artist, who turned 90 on May 31, traveled to Washington for a celebratory dinner at the Phillips Collection on Tuesday. The gallery is hosting an exhibition of his recent multi-panel works titled “Ellsworth Kelly: Panel Paintings 2004-2009,” on view through Sept. 22. We spoke by phone with the artist from his studio in Spencertown, N.Y., about his seven-decade experiment in abstraction.

How were the birthday celebrations?

They were fine. I’ve been having my birthday all month. They had a big party at the Museum of Modern Art. Renee Fleming sang “Happy Birthday” to me. She was sitting on my left during the dinner, and she would lean over and test her voice every couple of minutes. She’s an old friend and I’m glad she did it. The dinner [at the Phillips] was nice as well.

You’re 90 and still making art. Some might wonder when you’ll slow down or retire.

Artists don’t retire unless your limbs go! You expect that you’re not going to be the same person you were at 20 or 40 or 60. Things change. But art is all that satisfies me. To be able to create. I don’t know where it comes from, but it’s a need.

I’ve always wondered whether your service in the Ghost Army [the Army’s tactical deception unit that employed artists during World War II] affected you. Did it influence your work?

No, except that I was able to get on the GI Bill right afterwards in 1946. I went to Boston to attend the [Museum of Fine Arts] school. I learned to paint and draw from the nude. They weren’t interested in contemporary work, so I went through a year and a half of that and decided to go back to Paris.

Is that when you started making abstract works?

Well, they also taught painting from the nude, so most of the time, I was drawing on my own. That’s when I discovered what I wanted to do was different. I wanted to paint bright colors, where each color had its own panel and structure.

Your works were markedly different from your contemporaries in the ’50s and ’60s.

I didn’t want to paint what I saw with my eyes; I wanted to invent something I hadn’t seen before. Pollock, de Kooning and Rothko were abstract expressionists; artists in Paris and New York were doing action paintings. When they painted a picture, they found the painting by doing it. I started not doing that around the same time. I was beginning to think about what I wanted, to have an idea that came to me.

Some artists dabble in multiple styles, but you’ve remained committed to abstraction your whole life. Why?

I was tired of paintings of people! I wanted something you could investigate. I wanted people to see the depths of the painting rather than try to discover the content, the Liz Taylor or Marilyn Monroe. My content is color and form.

After living in New York in the ’50s and ’60s, you left for Spencertown in 1970. Do you think leaving New York helped you maintain your focus?

Artists have to make it in New York because that’s where the energy is, but when you feel like you’ve achieved something, you can leave to continue your own vision. . . . And since I’ve been up here, I’ve made bigger sculptures because I have a large studio. But at my age, I’m not doing big things.

Well, the panel paintings at the Phillips are large. They look like they were created for that exhibition space.

[Before] every show I do, I ask for the plans so I know the room, the measurements and the size of the walls, the doorways and where the windows are. [With the panel paintings] I wanted to present the paintings on their own walls. I want them to come out and visit the person who’s looking at them. I want the red to speak to you.

It must be shocking to look back on how the art world has changed since you began your career.

It has changed. In America, the best art is always too expensive. The art market gets in the way because ordinary people can’t afford the paintings, the ones that sell for $50 million. I always say, [for an artist] it’s like being in a prize fight somehow. You’re in the ring, and you’re battling the critical world in some sense. Sometimes you win, sometimes you lose, but you don’t feel like you’ve lost. Twenty years later, it sells for several million dollars. That’s why you have to stick to your guns and continue to be exhilarated by what you do.