When Cynthia Freeman finished writing Portraits, a 677-page saga of a Jewish family, she anxiously showed the manuscript to her mother. "I needed her approval," said the author. "Darling, it's very good," Sylvia Freeman told her daughter. "But I'm afraid it will never be a success. There isn't enough sex in it."

For an octogenarian, Mrs. Freeman is plainly a contemporary thinker, but Mother doesn't always know best. Portraits became a hardcover best-seller earlier this year and the paperback version is now No. 2. "There I was right up with Robert Ludlum and John le Carré," boasts Freeman, 65, whose first three novels did well in paper but never achieved blockbuster status. "I love winning."

She's at it again. Freeman's latest novel, Come Pour the Wine (Arbor House, $12.95), appeared on best-seller lists five weeks before the official publication date. The book's message is that women, like wine, improve with age. "Love...is so much better, more gentle, more tender," trills its middle-aged heroine. Sorry, Mother Freeman, but there's still not very much sex.

The author, who was born Beatrice Cynthia Freeman, grew up in San Francisco, where her German immigrant father struck it rich in real estate. With her English mother's encouragement, she had read Hamlet by the age of 11. "I would be called a gifted child today," Cynthia says, "but there was no place in school for me then. I went to the sixth grade, period. That was the end of my formal education."

At 18 she married Herman Feinberg, now a retired San Francisco urologist. She fell in love with him at 15 (he was her grandmother's doctor) "but it took him three years to notice me," she sighs. After their son and daughter were in school she became a successful interior decorator. Then she was struck by a rare intestinal illness that forced her to undergo surgery on and off for five years. "I weighed 99 pounds and I knew I couldn't continue with the decorating," she says. "But I did have the strength to pound typewriter keys." So at 55 she began writing what eventually became a 1,450-page manuscript. "For God's sake," moaned the children. "Are you writing the Bible?"

In fact it was the first of her family sagas, A World Full of Strangers, which was published by Arbor House in 1975 after four other firms had rejected it. Professionally, she decided to use her middle and maiden names on the dust jacket.

"I'm up at five in the morning because I like to work when my head is clear," she says. After breakfast at a doughnut shop near her Pacific Heights home, she plunges in and writes "all through the day like a busy bee. I don't lead a very interesting life."

Still, on a recent trip to Honolulu she took disco lessons while her daughter Nini, now 45, "was having massages." Freeman chuckles, "I gyrate a lot. Isn't that good for a 65-year-old lady?" In spite of such comments, the author fumes at the patronizing term "senior citizens." "There's no way I could have written my first book at 30," she notes. "I tell that to people my age because I want them to know you don't stop being productive."