This change which starts in July 2013 will allow Canadians who are turning 65 to delay taking the OAS pension. For each year that they delay, they will get an increase of 7.2%. In other words, if one is gainfully employed and wants to have a little bit more in retirement, one will have the flexibility of deferring the OAS. At the end of five years, that will be 36% more. It's an actuarial adjustment. That percentage was determined by the Chief Actuary of Canada. It takes into account that you will be receiving, in all likelihood, the benefit for a little less long, but you'll be getting more. It's a lifelong fully indexed benefit.
On April 30th, 2013. See this statement in context.