At 79¾ years of age, Judith Viorst feels qualified to speak – or at least write – from the perspective of someone in her eighties. Viorst, author of 36 books, is not apologizing for her somewhat premature 37th, “Unexpectedly Eighty and Other Adaptations” (Free Press, $17).

“I did not intend for this book to be out so soon,” Viorst says, speaking from her home in Washington, D.C. “I started thinking a lot about 80 when I was 75. I told myself if I thought about 80 ahead of time, I wouldn’t go onto cardiac arrest from the shock of reaching 80. The poems came pouring out.”

To her relief, most of the poems were not “organ recitals,” laments about the betrayals of the body. Instead, the book covers musings on spoiling grandchildren, driving at night, memories of love in the back seat of a car and fear of the great outdoors. A recurrent theme throughout “Unexpectedly Eighty” is the simple celebration of life.

“There is a vast difference between youth and age,” says Viorst. “When we are young, we think there are yes/no, black/white, on/off answers to the big questions of life. One way to understand the complexities of life is to understand that for many questions, the answer is all of the above. In other words, life is not about seeing the glass half empty or half full. The point is that you have a glass.”

Viorst has written eight collections of poems for adults and eight books of nonfiction, including her bestseller, “Necessary Losses.” Viorst also is the author of 19 books for children. “Lulu and the Brontosaurus,” Viorst’s newest children’s book, was published in September.

“I am so in love with this book, I can hardly stand it,” says Viorst, laughing. “Lulu is a pain-in-the-butt girl, a spoiled brat, an only child who wants what she wants when she wants it – and she wants a brontosaurus. In the book, Lulu goes into the woods, has many adventures and finds a brontosaurus. That’s all I’m telling you.”

Viorst did tell that the poem “House of Cards” in “Unexpectedly 80” is about Olivia, one of her seven grandchildren. The poem speaks of time spent with a grandchild, and the hope that the girl will always remember building a relationship with her grandmother. Another of Viorst’s favorite poems in the book pays fond tribute to her mother, Ruth June. “I felt I gave her her due,” says Viorst.

“Revelation” is about successful cataract surgery, “Exceedingly Eighty” is a riff on the phrase, “Eighty is the new 60.” Not so, says Viorst. “I just got an email from a fabulous, vital individual who looks great in a bathing suit, an 80-year-old woman going in on Monday for a lung biopsy. That happens a lot more often at 80 than 60.”

Reflecting on the decades Viorst has chronicled in earlier books, she notes that she is most surprised at what the later years have to offer. “At 60, 70 and now 79¾, I have been surprised how much better these decades are than I ever expected. They are rich with possibilities, sweet with old friendships. There are too many pills and a lot of knee replacements and backaches, but there also is a lot of good stuff.”

Among the good stuff is Viorst’s 50-year marriage, close relationships with her three sons and their families and the fact that many of her friends are still alive. “Eighty is not a downer. But you do have to love this day, love this moment. Don’t let any sunset or grandchild or bird or autumn leaf pass you by. Notice everything and live it all.”

“Everything” includes sharing Metamucil, taking classes in senior Pilates and accompanying one another to CAT scans and blood tests, all part of Viorst’s poem “Fifty Years Later.” She notes, “I think the Jews are survivors to some extent because they use humor to get them through. That said, the issues I write about are everyone’s.”

Viorst then reveals her all-time favorite fan letter. “I received it many years ago. A reader wrote to say that though she was a plump, blonde Methodist farm lady from the Midwest and I was a thin, dark, Jewish woman from the East Coast, we lived the same lives.”

Judith Viorst

WHO: Author

of “Unexpectedly Eighty and Other Adaptations”

WHEN: 1 p.m. Wednesday,Nov. 17

HOW MUCH: $18