Ludwig uses people too young to carry as a control group for a state that has instituted right to carry laws. I don't buy that as young people are often around people who do carry and may get some of the protective benefit. A better control would be a nearby state that has not changed its carry law. I'm surprised Ludwig didn't use the states that didn't change carry laws as a control group as that is what he used when evaluating the effects of the Brady Bill.
Here is
a good discussion of the effects of concealed carry on crime.
While the effects on crime rates are ambiguous, concealed carry can and does make a big difference to individuals.