There are many factors that strongly influence the etiology, development, and progression of cognitive decline in old age, mild cognitive impairment (MCI), and Alzheimer’s disease (AD). These factors include not only different personality traits and moods, but also lifestyle patterns (e.g., exercise and diet), and awareness levels that lead to cognitive decline in old age. In this review, we discuss how personality traits, mood states, and lifestyle impact brain and behaviour in older adults. Specifically, our review shows that these lifestyle and personality factors affect several brain regions, including the hippocampus, a region key for memory that is affected by cognitive decline in old age as well as AD. Accordingly, appropriate recommendations are presented in this review to assist individuals in decreasing chances of MCI, dementia, AD, and associated symptoms.