Using data from the Centers for Disease Control and Prevention's Web-based Injury Statistics Query and Reporting System, we analyzed trends in firearm suicide across the life course, comparing age-related trends over time (2015-20 versus 1999-2014) and stratified by differences in state firearm policy environments. Overall, we found stable trends in firearm suicide rates across the life course, although with higher overall rates across all age groups in 2015-20 versus in 1999-2014. Ages 14-16 was the only age group with an accelerating life-course trend in firearm suicide rates in 2015-20 versus in 1999-2014. The state policy environment was associated with significant differences in firearm suicide, with an average of 4.62 more deaths per 100,000 people per year in states with less- versus more-strict environments. This was in contrast to nonfirearm suicides, for which we observed no consistent differences between states. The largest overall differences in firearm suicide between states occurred in adulthood through middle age. These findings can inform further research on health care-based approaches to reducing firearm suicide, such as health care screening for firearm ownership, screening for suicide risk among firearm owners, and motivational interviewing to promote safe firearm storage.