High school shooting in Parkland FL

[henryp]

In my humble opinion, the one single thing that would reduce the homicide rate the most in the USA would be to stop the war on drugs and shift to a health-oriented approach to abusers. I doubt that would reduce mass shootings in schools significantly though.

Raising the minimum age to 21, requiring a violent-crime free criminal record and no prison time in the previous ten years, and a psych eval if you have mental problems might, though.

I'd remove the violent from there.... just crime free criminal record... and confiscation as soon as that record became less free.
Periodic Psych and medical eval. Do you want someone who develops Parkinson's to handle the arsenal he's amassed while Parkinson's free? (just an example)

https://www.thetrace.org/2015/07/gun-bac...s-failure/

To a degree, what your'e asking for is already in place.  The practicality of confiscation, though, is tricky.  You want to send a bunch of cops into black neighborhoods to confiscate their guns on a regular basis?  I can imagine some undesirable side effects to that plan.