Investigators said they're conducting a criminal investigation to determine whether the man's actions caused the fire and whether charges should be brought against him, the Los Angeles Times reported.
The fire, which began early Thursday afternoon, has burned almost 4,000 acres in the Pleasant Valley neighborhood near Reno and forced the evacuation of thousands of residents.
A woman died in the area of the blaze, possibly of suffocation, but authorities were still attempting to determine the cause of death, said Armando Avina, a spokesman for the Washoe County Sheriff's Office.
The Times said the elderly man, whom the newspaper did not identify, had been described by authorities as "extremely remorseful."
Crews were battling the blaze Friday night, when it was 65 percent contained, the Times said.
Nevada Gov. Brian Sandoval has declared a state of emergency, making the county eligible for federal disaster funds.
A November fire destroyed about 30 homes in south Reno, and a man died of a heart attack after alerting a neighbor the neighborhood was being evacuated.