figure 15.2 Substantial cognitive decline and age The occurrence of substantial cognitive decline is closely related to age. Fewer than 1 percent of all 60-year-olds have major neurocognitive disorders, compared with as many as 50 percent of those who are 85. (Information from: ASHA, 2015; Advokat et al., 2014; Ames et al., 2010; Nussbaum & Ellis, 2003.)