21 for handguns is federal law, as is 18 for long guns. Some states I believe have upped even long guns to 21. I don't think the age is the problem, there always seems to be someone who knew the person bought a gun, knew they were not right, might have said something might not, and no one properly investigated.
Now I'm not a fan of red flag laws as most are currently implemented as they remove due process completely a lot. I think the US needs to enforce the rules they have better and be very consistent. Our gun laws haven't changed much (they became a bit more restrictive) but guns have always been a part of the US. IMO other factors are driving gun violence and the vast majority (aside from suicide which is like half of gun deaths in the US) is a result of another already illegal activity.
I don't think violent games drive people to do violent things either. I'm clearly not a psychiatrist with no background in it but I just don't buy that a perfectly normal kid turns into a murderer by playing GTA or COD. If anything COD would make you want to join Special Operations military groups I would think. I forgot who said it earlier but I agree that there is something else there going on. Its possible they play those games to get their fix to whatever is really wrong and at some point it doesn't do enough anymore.
Just my thoughts.....But if they win these law suits things are going to change. Daniel Defense has never once marketed their firearms for killing innocent civilians. In fact I have never seen marketing where killing has ever been the focus. Its usually defense or be like the SEALs (which are good guys).