http://prospects.whl.ca/prospect-central-faqs/ "12. How many 20 year olds (overage players) can a WHL Club have on their roster?
WHL Clubs are allowed a maximum of three 20 year old players on their roster. Clubs having more than three overage players to start the season may continue to rotate them in and out of the lineup until a date determined annually in mid-October at which time they must declare the three that will remain on their roster. Other 20-year-olds become free agents and are made available to other teams in the WHL. Following that date, WHL Clubs may add an overage player, but if they already have three on their roster, then they must release one. January 10 of each year is the roster deadline and all players who are with a WHL Club on that date are there for the balance of the season."
I thought I read something about this in the Brandon Sun not that far back. Can't remember much about it though.