By using the age defense they have left the outcome ambiguous for others. I guess the heat generated in the press for this "senior citizen" forced the prosecutor to back off and drop charges. But the law itself remains. Would have been better for the other citizens of NJ if the case had gone to trial and a judge dismissed the charges and found the law to be improper.
Several points in response:
Clearly the amount of national and international attention to this contributed significantly to the use of "prosecutorial discretion" in this case.
However, there is also the likelihood that there were serious flaws in the case itself. And questions about the Sheriff's conduct and media disclosures. And then there is the little nuance of whether this particular 300 year old flintlock could potentially be considered "inoperable."
And, importantly, the Prosecutor's office, and the Prosecutor herself, are still embroiled in a number of rather embarrassing scandals that they need to dig out from in the public's eye. This may have been a large factor, combined with the above, if you've been following the local news and politics.
In the end, this case may just have been a big stinking pile that the Prosecutor just did not need on her desk. The wrong case at the wrong time.
Last point. Whether or not it would have been better for the citizens of NJ, it would certainly not have better for a 72 year old pensioner with limited ability to pay the legal fees to defend the charges in court.
Had the case gone to trial, I really don't think a NJ judge would find the law to be improper. Maybe dismissed the case on a technicality or on a motion (e.g. if the flintlock were per se found to be inoperable). More likely is the chance that the defendant would be found guilty and this aggressive NJ law would have found precedent extending back to 300 year old flintlocks.
Remember, they can prosecute in NJ for an unregistered BB gun. And that has not been overturned yet.