Could be that they were on the wrong meds. There's a ton of anti-depressant medications out there, the job of the doc is to find the right one/ones. On the surface, it looks like there's a correlation between the newer meds and the young age of the person taking them.
I don't think it wise to seize the firearms of a person just because of anti-depressant medications. There'd be a lot of LEO's that would be out of a job... maybe... huh?