tobnpr, If you can operate cnc equipment you are light years ahead of the poster my response was intended for. Having neither the experience/ knowledge, or financial means to, starting a specialized business of that sort is IMO not prudent.
Myself, being from the Empire/Vampire State of NY where we are being slowly bled to death I have seen a decline in the old type gunshop. While there is an increase in the type of shop that can sell you a firearm, mount a scope and that type of, I will call it " non technical " work there are very few " full service" gunshops here anymore. Couple that with extremely restrictive gun laws and I would have to say that NY is not a gun friendly state. In those states where firearms are widely accepted, such as Florida I would have to agree with you. The fact that you could take on general machine work should the " gun work " slow down is an added +.
In any case the young man mentioned previously needs to learn more about firearms work as well as the machining business before he quits carpentary. Do it, whatever it is as a hobby first. I would never tell anyone at any age to stop learning.