(CNN) -- I'm 45, and my son is 7.





Once in a while, I still get carded when I try to buy certain well-guarded cold medicines, so I was taken aback in recent months when two different strangers asked, "Is that your grandson?"





I was most surprised by the instant assumption, without an awkward pause or hesitation, as if grandmother was the only option. I was 38 when Jason was born -- not exactly a young mother, but nowhere near the age I imagine a grandmother to be.





Both incidents took place after I moved from California to Atlanta, a Southern city, and both times I was asked by fellow black women -- one about 21, and one who was my senior.





I thought about the incidents when I read a recent CNN.com essay by Rose Arce on being mistaken for her daughter's nanny. The essay inspired me to post my case of mistaken grandmother identity on Facebook, where I got lively responses ranging from "Are you kidding?" to makeover tips.





Had I let too many gray hairs escape my patrol?





Maybe the question shouldn't have surprised me, given the historically high teen birth rates and young grandmothers in the black community, especially in the South.





But I have since learned about a convergence of birth and child-rearing trends that make it harder to guess whether an over-40 caretaker is a grandparent or, like me, a more ... er ... "mature" mother.





First, experts say teenagers are having fewer babies.





"We believe evidence-based teen pregnancy programs work best," says Vikki Millender-Morrow, the CEO of the Georgia Campaign for Adolescent Pregnancy Prevention (G-CAPP), founded by Jane Fonda. "We also believe in giving the kids hope. Even with all the education in the world, if they don't believe their future circumstances are brighter than what they're seeing, what's the reason to delay?"





Georgia had the highest teen birth rate in the nation in 1995, but currently ranks No. 13, according to Millender-Morrow. And recent data shows that Georgia was one of 10 states -- including Mississippi, Florida and Arizona -- that had the most dramatic decreases in births to 15- to 17-year-olds between 2007 and 2009.





It's a national trend.





According to preliminary data from the Centers for Disease Control and Prevention's National Center for Health Statistics published this year, the birth rate for teens ages 15 to 19 had reached its lowest point in the nearly 70 years since the data has been tracked. Black births to teens ages 15 to 17 have plummeted since the 86.1 rate in 1991, for example, when the Hispanic rate was 69.2 (per 1,000 women).





Still, black and Hispanic teenagers still have a much higher birth rate than non-Hispanic whites. The February report shows that the birth rate per 1,000 teens for black teenagers ages 15 to 17 was 32.1 in 2009, and even higher at 41 for Hispanic teens -- compared with just 11 for non-Hispanic whites.





If more young people are weighing their life options -- with fewer "babies having babies" -- fewer grandparents are raising their grandchildren, right?





Wrong. More children are being raised by their grandparents.





U.S Census Bureau data from 2009, published in July, reports that the percentage of white and Hispanic children being raised by one or both grandparents doubled between 1991 and 2009, from about 1% to 2%. About 5% of black children are raised by a grandparent, a figure the Census Bureau says has remained constant since 1991.





Citing the impact of harsh economic times, the Pew Research Center's latest data from 2008 indicates that 2.9 million children were being raised primarily by their grandparents -- up 8% from 2000, and 5% from 2007.





Pew reports that the number of black grandparents serving as primary caregivers fell 12% between 2000 and 2008, but the number of white grandparents spiked 19%. The number of Hispanic grandparents becoming caregivers rose 14% during that eight-year period. According to Pew
What was Due asked? What age is she? What percentage of grandparents are raising children? What has Tananarive Due been asked? What age is Tananarive Due? Who are now raising more children? More children are being raised by who?
"Is that your grandson?" 45, latest data from 2008 indicates that 2.9 million "Is that your grandson?" 45, grandparents. their grandparents.
question: What was Due asked?, answer: "Is that your grandson?" | question: What age is she?, answer: 45, | question: What percentage of grandparents are raising children?, answer: latest data from 2008 indicates that 2.9 million | question: What has Tananarive Due been asked?, answer: "Is that your grandson?" | question: What age is Tananarive Due?, answer: 45, | question: Who are now raising more children?, answer: grandparents. | question: More children are being raised by who?, answer: their grandparents.