Long-term childhood adolescent and young adult (CAYA) cancer survivors may develop health conditions that often coexist at young adulthood or middle age and that normally occur in persons aged 65 years and older, including cardiovascular and musculoskeletal diseases, metabolic syndrome, and secondary malignancies, suggesting that a process of accelerated aging occurs. This chapter summarizes epidemiological evidence and physiological mechanisms of accelerated aging, and possible preventive measures to delay the process of accelerated aging in CAYA cancer survivors. Evidence is mounting that in addition to a high prevalence of specific and multiple aging-related chronic diseases (multimorbidity), CAYA cancer survivors seem to also have a higher risk of other aging phenotypes, including frailty, poor physical performance, and changes in body composition (low muscle and high fat mass). Risk factors for these aging phenotypes include treatment-related factors (cranial-spinal radiotherapy, anthracyclines), sociodemographic factors (higher age, female sex, low socioeconomic status), and unhealthy lifestyle factors (i.e., physical inactivity, obesity, smoking, excess alcohol consumption). The process of accelerated aging may be prevented or delayed by adopting and maintaining a healthy lifestyle, so that CAYA cancer survivors may live a life with optimal quality of life after cancer.