The two men who shot dead 18 people in separate incidents just days apart in California are the latest perpetrators in America’s long history of mass gun violence. But something about these public shootings, and the men held responsible, stands out.

The median age of mass shooters in the United States is 32. Yet the man who is alleged to have shot dead 11 people in Monterey Park on Jan. 21, 2023, before turning the gun on himself was 72 years old – the oldest mass shooter in modern American history, our records show. Meanwhile, the gunman who took the lives of seven more in Half Moon Bay two days later was also older than most — 66, the third-oldest in history.

We are criminologists who built a database of 191 mass shooters using public data. The shooters in our records date back to 1966 and are coded on nearly 200 different variables, including age at the time of attack. Our research shows that mass shootings – defined here as events in which four or more people are killed in a public place with no underlying criminal activity – have become more frequent, and deadly, over time.

Prior to the January 2023 Californian shootings, mass shooters were also getting younger overall. From 1980 to 1989, the median age of mass shooters was 39. Over the next two decades, it was 33. And from 2010 to 2019, it was 29.

Since 2020, the median age of mass shooters has come down to just 22 years old — mostly young men and boys who were born into or came of age in an increasingly divided America and carried out their attacks amid the disruption of a global pandemic.

Ages vary by shooting location, the data shows. Though mass shooters at offices, warehouses and houses of worship skew older, shooters at K-12 schools, colleges and universities tend to be younger – in large part because many school shooters tend to be current or former students.

Prior to the tragic incidents in Monterey Park and Half Moon Bay, just six mass shooters in our study were over the age of 60. The oldest was a 70-year-old who killed five people at an auto parts store in Kentucky in 1981. The list also includes the perpetrator of the deadliest mass shooting in U.S. history – a 64-year-old who killed 60 people at a 2017 music festival in Las Vegas.

The others were a 66-year-old who was supposed to turn himself in to serve a prison sentence but instead killed four people at the manufacturing plant where he used to work in Illinois in 2001; a 64-year-old who killed four barbershop and oil change shop patrons in rural New York in 2013; a 62-year-old who killed four people in 1997 in New Hampshire, including two state troopers and a judge; and a 60-year-old who killed six at a shopping center in Palm Bay, Florida, in 1987.

Nearly all of the over-60s perpetrators of mass shootings prior to the January 2023 Californian incidents were white men – just one was a nonwhite male. This differs in the Monterey Park and Half Moon Bay incidents, both of which are thought to have been carried out by Asian Americans.

Mass shooters over 60 also tend to have prior criminal records and to target their place of employment, or retail and outdoor locations in communities they knew well.

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