The Early Sessions, Book 5

"...for the dream experiments that we plan will enable you to accumulate in time a list of primaries...it will be shortly discovered that the physical organism does not age in sleep at the same rate at which it ages in the waking state. Aging, therefore, is not a primary... A recognition of the differences between primary and secondary conditions can however allow you to minimize the effects of the secondary conditions to some considerable degree."

Session 208, Page 70