It is mandatory that you convert all your RRSPs by December 31st in the year you turn 71. The latest you are allowed to take your first payment is December 31st in the year you turn 72, however, the payment must be at least the full annual minimum* amount.
Canada Revenue Agency stipulates that a minimum payment must be withdrawn from your RRIF each year and reported as income. *This minimum annual payment is taken from a schedule that is based on your age or the age of your spouse.
For more information, including the factors used, please consult the following link to Canada Revenue Agency's website: http://www.cra-arc.gc.ca/E/pub/tp/ic78-18r6/ic78-18r6-e.txt