One key is to check for OAS clawback...
If, with the RRIF, they are far from being hit with a OAS clawback,it may make sense to draw a little more than the minimum required... especially if more income will come on line when the youngest is 65, 67 or 71 for example. If they don't need all the income, put it into a taxable investment account...
Using the younger spouse's age as the minimum is fine (although I can't recall if you can use the age of someone as young as 60, so I am assuming yes here)... just withdraw a bit more until they hit at 20% income tax level... if more invome / pensions in future.