More older Canadians, including senior citizens, are using marijuana as fewer minors consume the substance, according to a new study released Monday by Statistics Canada.

The report shows that nearly five million Canadians used pot in 2015, a growing trend that also marks a demographic shift away from what was once "youth-driven" market in the 1960s and 1970s.

By 2015, less than six per cent of consumers were in the 15-17 year-old age group, compared to two-thirds of consumers who were 25 years old or older, according to the federal statistical agency.

"This study and others has shown recently that use of cannabis among youth has either remained stable or has declined whereas use among older individuals has increased," analyst Michelle Rotermann told CBC News.

The percentage of youth pot consumers has fluctuated over the years, but the 2015 figure marks the lowest in decades.

In 1960 an estimated 18 per cent of marijuana users were minors, which increased to 22 per cent in 1980, then fell to 12 per cent by 2000. By 2015, only 5.8 per cent of marijuana users were aged 15-17.

Additional data provided to CBC News from Statistics Canada shows there are fluctuations in youth consumers over the decades. Consumption rose in the 1970s, peaking at 495,000 consumers aged 15-17, then declining in the late 1980s and early 1990s.

The number of young consumers has declined in the past decade, with 283,000 minors using cannabis in 2015, down from 373,000 in 2005.

Prime Minister Justin Trudeau and other members of his government have repeatedly stated that the government's plan to legalize marijuana is to remove profits from criminals and to limit access to minors.

Today's report says there is a need to measure the economic and social impacts of legal weed as Canada prepares to legalize, regulate and restrict cannabis in July 2018.

Medical, recreational users

Right now, there is no systematic process in place for measuring pot consumption. The study released today relied on multiple data sources, including Statistics Canada surveys, collected for other purposes to estimate consumer habits.

It estimated 4.9 million cannabis consumers aged 15 and older in 2015, a figure that includes medical and recreational users. A steady decline in use among youth has been outweighed by increases among older persons, which have led to an overall increase in cannabis consumption.

Canadians consumed 698 tonnes of cannabis in 2015, up from 484 tonnes a decade ago, and up from 324 tonnes in 1995.

With an assumed price range of $7.14 to $8.84 a gram, the total value of cannabis consumption in Canada for 2015 was between $5 billion and $6.2 billion.

The Liberal government hopes to restrict access of marijuana to minors when it becomes legal in July 2018. (Jim Mone/Associated Press)

Baby boomers big consumers

Older Canadians consume bigger quantities, according to the report.

"The compositional change in the cannabis market is consistent with a change where the baby boomer cohort was exposed to cannabis in high school and university, and carried a preference for cannabis consumption with them as they aged," the report notes.

"The rising trend occurs as boomers, and the cohorts that followed after them with similar exposure and preferences, replaced the war generation, which had different preferences with respect to cannabis use."

Recent data for mid-2000s onwards shows a rising rate of cannabis consumption among senior citizens aged 65 and older.

When the government tabled its legalization bill in April, Bill Blair, the former Toronto police chief who is Trudeau's point man on the pot file, said from experience the use of cannabis among young people is "among the highest in the world."

"I believe that we have to do a better job of protecting our kids," he said at the time.

Then-health minister Jane Philpott, now minister of Indigenous services, also said current laws are not preventing youth from using marijuana.

"The prohibition approach has not deterred young adults from using this product. The current approach is not working," she said.

Last week, federal Finance Minister Bill Morneau reached a deal with his provincial and territorial counterparts on excise tax-revenue sharing. The regime gives the provinces 75 per cent of the revenue, and caps the federal share at $100 million for the first two years.