Background & Objective: Gender inequalities in society result in gender differences in the social determinants of health and health risk factors, and have lifelong health consequences. However, little research systematically examines the magnitude and nature of gender differences in health across the life course. Methods: We used data from the Global Burden of Disease Study (GBD) 2021 to conduct a descriptive analysis of gender differences in the top-20 causes of male and female Disability-Adjusted Life Years (DALYs) globally and across world regions for four age groups (10-24, 25-49, 50-69, and 70+ years). Results: Across the lifespan, female DALY rates are higher than males (p<0.05) for mental, neurological, and musculoskeletal disorders globally. For depressive, anxiety, and headache disorders, the female-male gap emerges at an early age and continues over the life course. The gender gap in low back pain widens with age and is highest at 70+ years. Girls and women aged 10-49 years have higher DALYs due to HIV/AIDS compared to men, and the most pronounced gap is in sub-Saharan Africa. On the contrary, for several conditions with a higher male burden (p<0.05), gender gaps emerge after 50 years, for e.g., for COVID-19, ischemic heart disease, and lung cancer. Among younger males (10-24 years), road injuries are the top cause of global DALYs, with the largest male-female gap in Latin America. We also find that women and girls are more affected by conditions with a higher morbidity burden throughout their lifespan. On the other hand, men and boys of all ages bear a disproportionate mortality burden. Conclusions: Our study highlights the need for policy interventions to promote well-being and reduce gender disparities in health at all stages of life, in line with the United Nations Sustainable Development Goals (SDGs) 3 and 5.