New laws in California and New York might stop people from 3D printing guns
It absolutely, positively, will not do that. If someone wants to print a gun, no legislation is going to stop them. It could at best, slow them down by maybe an hour, as they find, download and install different firmware for their printer.
If you want to prevent people from printing guns, you'll need a different tactic, because that won't do it.
Most of the advantages don't come from being over 40, but rather, from the experience of having lived over 40 years. What you have is knowledge and perspective. You can make better choices, fall into fewer traps. It's that "wisdom" thing you may have heard of.
Also, as most people over 40 have been working for some time now, many of us (though definitely not all) have reached a different phase of their life financially. In my 20s, when things went wrong it was generally like "well, this is my life now", but in my 40s when something goes wrong it's more often like "ok, how much will it cost for this problem to go away?". And don't forget, with all of that wisdom we have, sometimes we can just solve the problem, but when that won't work, throwing money at problems is generally effective.
Finally, I think someone already said it, but it's worth repeating. You stop giving a shit about a lot of things, and it's liberating. It feels like honesty and confidence and contentment.