PHILADELPHIA &#8212 Brittney Exline is too young to drive a car or even go to an R-rated movie, but the 15-year-old probably won’t have much time for those things anyway now that she’s starting her first year of college.

Exline begins her Ivy League career Wednesday when classes begin at the University of Pennsylvania.

Despite the age difference with her 17- and 18-year-old peers, she said she doesn’t really notice it – and neither do they.

“I didn’t tell people right off the bat that I was 15,” Exline said. “A lot of people were pretty surprised.”

Exline grew up in Colorado Springs, Colo., where from an early age her intellect was both evident and unexplainable.

At 8 years old, she was in sixth grade; by 13, she had finished high school math. She turned 15 in February and graduated a few months later.

But she’s not preoccupied with how unique her accomplishments are.

“I wouldn’t even really realize that if people didn’t tell me,” she said.

Exline’s resume includes years of dancing and singing – hobbies she hopes to continue at Penn – and a couple of teen pageant titles. She excels at math and science, but is really interested in politics, so she enrolled in a Penn program that will award her degrees from both the engineering and liberal arts schools when she graduates in 2011.

“Her motivation, discipline and maturity provided clear evidence that despite her age, she was ready to travel halfway across the country and thrive in Penn’s rigorous academic environment,” Eric Kaplan, interim dean of admissions, said in a statement.

Exline’s mother Chyrese, a geriatric supervisor, said her concerns about her daughter’s freshman year are probably no different from any other parent’s.

She and her husband, a supply supervisor, and 10-year-old son are already counting the days until Exline comes home for winter break.

“We did our best to prepare her,” Chyrese said.

Exline has already been on the Philadelphia campus for about a month, participating in a pre-freshman program to get acclimated to the school. Program counselor Noemi Maldonado described her as “extremely outgoing, very social, very friendly, very mature for her age.”

Miguel Gonzalez, another program participant, said he and about a dozen other incoming freshmen were hanging out late one night earlier this summer when Exline revealed her age.

“She’s really cool for a 15-year-old,” said Gonzalez, who turns 18 later this month. “We were surprised, but I don’t think it’s too shocking.”

There have been much younger college students: Jessica Meeker enrolled at Penn State two months before her 13th birthday, graduating in 2004 at age 16.

Exline will be a 19-year-old graduate if she stays on the four-year track.

She plans to take advantage of as many opportunities as possible between now and then, including studying abroad her junior year.