Mom's 57th Birthday Gift - Twins!

Aleta St. James, the sister of Guardian Angels founder Curtis Sliwa, is due to deliver twins this week, just three days shy of her 57th birthday.

"It's never too late. You are never too old," said St. James. "It's just in your mind."

St. James, a motivation speaker who helped her brother set up the crime-fighting group in the 1970s, became pregnant after in-vitro fertilization.

The Manhattan resident, who will be a single mom and 57 on Friday, will deliver her twins — a boy and a girl — by Caesarean section at Mount Sinai Hospital on Tuesday.

She already has the babies' names picked out: Gian and Francesca.

And what does her brother, a radio host, think about his sister's decision to have children in her 50s?

"I really can't think of anyone more capable of taking on that responsibility to show other women who never thought that they could have kids," Sliwa said. "She'll be a great mother."

CBS News Correspondent Sharyn Alfonsi reported on The Early Show that in the last two decades alone, the number of women older than 40 having children has more than doubled.

"It's a complete phenomenon in our day and age, right now, sure," said Jann Blackstone Ford, who wrote a book about mature moms.

Ford said celebrities like Susan Sarandon, Jane Seymour and Geena Davis made having children well into their 40's stylish.

"While there are some increased risks in older women having babies, it's not that significant and most of the things can be dealt with," Dr. Jamie Grif told Alfonsi.

Even hours away from giving birth, St. James said she's in it for the long haul.

"Physically I feel very energetic, so at 70, I'm not going to be like a 70-year-old," she said. "I'm going to be young and vital."