You're correct. The normal age for receiving a retirement pension from the Canada pension plan is 65. However, you may draw your pension starting at the age of 60, but it will be subject to an actuarial penalty, or wait until you're 70 and get an actuarial increase.
There's no further benefit for deferring payments beyond the age of 70. As a result, people receive the largest amount they can possibly get at 70. That's why the age of 70 was chosen; there's no further reason to wait after that age.