This is what the instruction guide says:
Type A
The child is under the age of 22 and is single (not married and not in a common-law relationship).
Type B
The child has been continuously enrolled in and in attendance as a full‑time student at a post-secondary institution accredited by the relevant government authority and has depended substantially on the financial support of a parent either:
- since before the age of 22, or
- since marrying or entering into a common-law relationship (if it happened before the age of 22).
Type C
The child is 22 years of age or older, has depended substantially on the financial support of a parent since before the age of 22, and is unable to provide for himself or herself because of a medical condition.
