The older population is itself ageing, because of declining mortality and increasing lifespan at advanced ages. The median age of the 65+ population has increased by almost three years since the early 1950s, from 71.4 years to 74.2 years in 2006, and is projected to exceed 77 years by 2051. This is also confirmed by the growing concentration of population at ages over 84 years. Under projection series 5, the number of New Zealanders aged 85 years and over is projected to more than quadruple, from just under 57,000 to 322,000 by 2051. Those aged 65–74 years made up 70 percent of all residents over 64 in 1951, 53 percent in 2006, and are projected to drop to 40 percent by 2051. By contrast, over the same period, the share of those aged 85+ rose from 3.9 percent in 1951 to 11.7 percent in 2006 and is projected to rise to 24 percent in 2051.