CPC-M is required by law to lock in the age at the time the application is RECEIVED. This is from OP Manual 2:
The lock-in of age for dependent children is the day CPC-M receives a completed IMM 1344AE
and correct processing fees. Dependent children must be less than 22 years of age when the
sponsorship application is received.
Under 22 years means up to and including the last day before the dependent child's 22nd
birthday.
Offices must date-stamp application forms as soon as they are received.
The lock-in of age for dependent children is the day CPC-M receives a completed IMM 1344AE
and correct processing fees. Dependent children must be less than 22 years of age when the
sponsorship application is received.
Under 22 years means up to and including the last day before the dependent child's 22nd
birthday.
Offices must date-stamp application forms as soon as they are received.