Quoted:
CRS Points -
A candidate who reports an age difference between the time they receive an invitation to apply (ITA) and the time they submit an application for permanent residence (APR) could lose points that were awarded to them for their age, which is one criterion used to establish their rank relative to other Express Entry candidates, and to determine their eligibility to receive an invitation to apply. Applications can be refused for this reason despite the applicant's ability to meet regulatory requirements of the economic immigration program for which they have applied.
A temporary public policy will permit the exemption of candidates from application of section 11.2 of the IRPA only if the loss of eligibility or qualification has occurred due to aging of the applicant between the submission of an invitation by IRCC and the receipt of the resulting application by IRCC.
SOURCE: http://www.cic.gc.ca/english/department/laws-policy/exempt-applicants-pr.asp
Accordingly this exemption will apply to those individuals whose ranking may change due to age from the time an invitation to apply to OINP was sent and receipt of the APR application.
The OINP exempts applicants from drops in CRS scores that are related to their age. In this regard, we will consider your age at the date your notification of interest was sent.
Consequently, you may be eligible to apply even if your score has fallen below 400 points but only if it is because you changed age between the time you have received your PT Notification of Interest from OINP and the time you have submitted your application for permanent residence to Immigration, Refugees and Citizenship Canada (IRCC).
It is the only exemption for having a score below 400 points. Otherwise, you must maintain a minimum score of 400 points on the Express Entry Comprehensive Ranking System (CRS) through the Ontario processing stage and your Application for Permanent Residence to IRCC.