Of note, Whitehorse and Yukon have very similar ratios (because the majority of the Yukon population lives in Whitehorse).
HJ appears to historical had a proportionally higher seniors dependency ratio at 0.25 in 2017 compared with Whitehorse at 0.17 and Yukon at 0.18.
Youth = 0 to 19
Working Age = 20-64
Seniors = 65+
With regard to Dependency Ratio, Stats Can says:
Importance of indicator
A sizeable share of seniors aged 65 or older and children and youth younger than age 20 are likely to be socially and/or economically dependent on working-age Canadians, and they may put additional demands on health services. The demographic dependency ratio measures the size of the "dependent" population in relation to the "working age" population who theoretically provide social and economic support.
The majority of this data is sourced from the Yukon's Socio-Economic Portal