About 90% of women who have normal blood pressure at the age of 65 will develop hypertension by age 85.
Vasan R, Beiser S, Seshadri S, Larson M, et al. Residual Lifetime Risk for Developing Hypertension in Middle-Aged Women and Men: The Framingham Heart Study. JAMA. 2002; 287(8): 1003-1010. http://jama.ama-assn.org/cgi/content/abstract/287/8/1003