Mental illness among older adults has become a growing public health concern due to the increasing aging population worldwide. This paper examined the factors influencing mental illness among older adults, common mental health disorders experienced in later life and possible preventive and management strategies. Aging is often associated with challenges such as social isolation, loss of meaningful roles, bereavement, chronic illness, reduced mobility and cognitive decline, all of which may contribute to poor mental health outcomes. Evidence indicates that depression, anxiety disorders, dementia and psychosis are among the most common psychiatric conditions affecting older persons. Additional risk factors include poor nutrition, medication interactions, substance abuse, financial difficulties, loneliness, and lack of adequate family or community support. The paper also highlighted early warning signs such as persistent sadness, confusion, memory loss, withdrawal from social activities, sleep disturbances and unexplained fatigue. Findings revealed that mental illness in old age is often underdiagnosed or untreated because symptoms are wrongly considered a normal part of aging. Effective prevention and management require early detection, social support systems, healthy lifestyles, professional mental health services, and policies that prioritize the wellbeing of older adults. It was concluded that promoting mental health among the elderly is essential for improving their quality of life, independence and overall contribution to society.