http://www.cic.gc.ca/english/resources/manuals/op/op02-eng.pdf - page 15 said:
In order to meet R2(b)(i) of the definition of “dependent child”, a child must be under 22 years of age and not a spouse or common-law partner on the date when the IMM 1344AE is received by CPC-M, and not a spouse or common-law partner when the visa is issued, and when they arrive in Canada.
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R2(b)(ii) & (iii) describe children over the age of 22 who may be considered dependent children if they are substantially dependent on their parents for financial support. This includes full-time students enrolled in accredited post secondary institutions or children with a physical or mental condition. In such cases, officers must ask for documentary evidence of full time attendance at school, evidence of the institution's accreditation with the relevant authority, evidence of the physical or mental condition and evidence of financial dependency on parents.