Okay, say what you want about my math, but here it is anyway...
If in 2018, the average age of a mass school shooter is 21 and if we subtract 21-years from the current year (2018 - 21) we get the year 1997. I got that approximate age by adding the ages of shooters listed in this NY Daily News.
If, in 2018, the average age of all mass shooters is 35, and, if we subtract 35 from the current year (2018 - 35) we get the year 1983. I got that approximate age by adding the ages of all the mass shooters listed in a Wikipedia table.
Imagine today had we accepted our responsibility for developing comprehensive #CommonSenseGunLaws in 1949 at the time of the Camden shooting or in 1966 when the University of Texas tower shooting occurred.