The bicyclist, Jim R. Price of Highlands Ranch, died Friday, two days after the accident.
"We do not believe it was an intentional act, but it was inattentiveness to the roadway," said Lt. Alan Stanton, spokesman for Douglas County Sheriff's Office.
"The investigation showed that he was text-messaging on his cell phone" at the time of the accident, said Stanton.
The driver could face a charge of careless driving resulting in death, Stanton said. Under Colorado law, the teen could face up to a year in prison.
It was the second time Price, an avid cyclist, had been hit by car. He suffered a broken ankle two years ago when he was hit while riding on a bike path. His wife, Shirley, said he had been especially mindful of cars since then.
Shirley Price wasn't angry with the teen. "I feel sorry for the teenager," she said. "It was a stupid mistake," she told the Rocky Mountain News.