The 6ft 9in aspiring model also has an inseam of 43 inches and has to stoop to avoid banging her head when walking through doors.
Maci was only 19 inches when born, but a series of growth spurts meant she rocketed to 5ft 7in by the time she was nine years old.
Maci’s mother Trish, 55, told Barcroft TV: “I realized that she was taller than the average kid at about 18 months, when she was already 2ft 11in. “She was at a Mother’s Day Out and I went to pick her up and she was already a head above the other children.
“There’s a picture of her standing next to another little girl and she looked like she was two years older.
“There were four or five years that she grew like five inches in a year, which is a lot. She has always had long legs. I used to think I had long legs but not anymore.”
Height is definitely in Maci’s genes - while mother Trish is only 5ft 7in, her father Cameron, 52, is 6ft 5in and her brother Jacob, 17, is 6ft 3in.
And despite being proud of her height, teenage Maci says she is thankful she has stopped growing – at least for the time being.
She told Barcroft TV: “When I stopped growing in ninth grade, I was really relieved. Because when I was younger, I'd get those growing pains in my legs that were so terrible.”
Maci has embraced her lengthy limbs, but says there are downsides that come with having the world’s longest legs. She said: “There are definitely negatives to having such long legs: hitting your head walking through doors, getting into cars, trying to find clothes that fit.
“I don't wear certain things like jeans because I can never find any that fit me. I do like to go to this one store in Colorado and they have extra-long yoga pants that I get.”
Maci’s size also means she receives a lot of unwanted attention at school and when she is out and about in public.
She said: “I know when high school starts again, there's going to be a new batch of freshmen who don't know who I am. So they're definitely going to stare and be like, "Wow, she's so tall."
“Also when I go to the mall, there's just a bunch of people staring at me. There's people that will get their phone out and try to take a picture without asking. “I kind of just like stare at them like, "Are you serious?"”
However, Maci is hoping to convert her long legs into modelling jobs and says there are upsides to her height.
She said: “When you're in a crowd and you're with friends and can't find them, you can just look over everyone and be like, "There she is." And then in sports it’s valuable, being tall, it’s great for blocking.”
Maci’s record has yet to be officially verified by the Guinness Book of World Records, but for Maci’s mom Trish, her daughter’s height is secondary to the strength of her character.
Trish said: “She once said to me: “Mom, I hang out with everybody.” She goes, “I am good with the popular girls, I am good with the not so popular girls. I just hang out with whoever I want to hang out with.
“She is very good about being comfortable in her own skin. And I probably struggle more than she does with accepting the fact that people are always staring at her and trying to take pictures of her or being rude to her. She is a pretty strong girl.”