Hours later, after an outcry, Stanley Casson, of Prestwich, Greater Manchester, was released on bail pending an appeal.
Judge Gerard Humphries at Manchester Crown Court told Casson, who had an unblemished driving record from the age of 17, that only a prison sentence could "properly reflect his criminality".
Casson's Ford Scorpio ploughed into Bridget Wood, 78, and her six-year- old granddaughter, Hollie Williams, last October as they crossed a four- lane highway in Blackley with Hollie's brother, Ryan, 13, after a shopping trip.
Ryan escaped injury.
The court heard that the accident took place at dusk, in fine weather. Casson, who admitted causing the deaths by dangerous driving, was on his way home after helping out at the family leather goods business in Oldham.
A witness, Beverley Aspen, who was driving behind him, said: "I looked ahead and could clearly see three people crossing the road from the nearside pavement. I remember one had white hair and they were in the middle of the road, near the white line.
"Suddenly I could see lots of articles flying in the air in front of the first car and knew immediately that the car must have hit the people.
"I remember thinking, `how could the driver not possibly have seen them'. I could see the little girl lying in the road."
After the accident, Casson was given an eye test by police and was unable to read the registration of a vehicle from 20.5 metres, as is required of candidates taking driving tests. He could only read it from 18.9 metres.
The judge told him yesterday: "Loss of liberty will hit you harder than most because of your age. I make the sentence much shorter than it would otherwise have been.
"There was a failure on your part to see these two people. It did not involve recklessness, speed or taking a risk."
Casson told police after the accident that he usually left work in daylight because he did not like driving at night.
According to a report in April by Her Majesty's Inspectorate of Prisons and Probation, there were 820 men and 17 women over 60 in the prison system.
The AA said yesterday that elderly drivers were usually safe and conscientious behind the wheel."Older drivers are responsible for only a small minority of accidents," a spokesman said. "They are a fairly safe group of drivers and the accident risk they pose on the road is exactly the same as for a 25-year-old."