Supposedly StatsCan is following this guideline.
"The 15 to 24 age range used by
Statistics Canada is the global standard set by the International Labour Organization (ILO) to specifically measure the transition of individuals from full-time education into the workforce."
"However, because the 15-24 bracket lumps together high-schoolers looking for part-time work with university graduates starting their careers, economists often break it down further (e.g., separating 15-19 from 20-24) to get a clearer picture of the job market"
The range of 15-19 and 20-24 is alot more logical and its a break (especially under the old 'Grade 13 era') of those in high school and those out of high school.