Life annuity payments change due to some uncontrollable factors such as your increasing age and the amount of your savings. (Read annuity article)
Then there are the factors for life annuities over which you have no control.which can generally be headed under ” demand for money “And these factors include mortgage rates,short and long term interest rates and the state of the economy.If these 3/4 items are not doing well,companies won,t have a large demand for funds,so life annuity payments will suffer.
And while all this is happening,you are getting older and so will receive a smaller number of life annuity payments,even if you get a higher monthly payment.To try to get a greater overall return by waiting to take life annuity payments is a very dangerous game.