Blaney, the son of Sprint Cup driver Dave Blaney, broke the age record of 20 years, 18 days set by Kyle Busch in 2005 at Charlotte.
"This is pretty unbelievable," Blaney said. "Hopefully we can get a few more here."
Blaney held off Ty Dillon by less than a car-length after a restart with three laps to go on the 0.875-mile track. He's the seventh first-time winner this season.
He said he had trouble with restarts throughout the race but was able to figure it out at the end.
"Whatever I did, starting fast or starting slow, I could just not keep the tires from spinning," Blaney said. "I was able to at least hold my own into one and that was really all we needed to do."
His father was there to see the whole thing.
"He did it all right," Dave Blaney said. "(Crew chief leader) Doug (Randolph) made a really good call on tires there midway through the race that ended up being the perfect call and got him in position. And (Ryan) brought it home."
Todd Bodine was third in the 200-lap race slowed by nine caution periods that took up 54 laps. The 48-year-old Bodine said he was happy for the young Blaney, calling him a "good, shy kid."
Bodine said experience didn't make much difference at the end of the race.
"At that point, it's going to be who's got the better truck and the better tires and the bettter position," he said. "It's fun to see. Obviously, we would have liked to win, but it's fun to see these kids coming up and doing so well."
The 20-year-old Dillon took over the season points lead. Timothy Peters, the points leader entering the race, was 19th to drop eight points behind Dillon. James Buescher placed 17th and moved into third place, 11 points behind the leader.
Dillon had his 13th top-10 finish in 15 starts. With seven races remaining, he's chasing the points title and his brother's record. Austin Dillon, racing in the Nationwide series, became the youngest champion in Trucks history last season.
Parker Kligerman, fourth in points, won the pole and led for 107 laps, but blew two tires with 21 laps to go and finished 23rd.
On the 96th lap, Caleb Roark lost control and slammed into the wall and bounced into the path of Justin Lofton, who began the day fifth in points. Lofton couldn't avoid the wreck, spun into the wall and dropped out of the race, finishing 31st.
Blaney made his Nationwide Series debut at the track this year, finishing 10th.