In A Curious Thing, Hook fends off the flying monkeys with an old fashioned flintlock pistol. But there should be nothing that advanced in the Enchanted Forest, no early form of gun has ever been shown; and Hook didn't recognize the gun in 2.11. So my theory is that after Regina brought everyone back to the EF in 3.11, some people that lived in Storybrooke must have remembered how guns work (and some people could have worked in a gun shop in SB and know how to build them). So with EF's limited resources, some flintlock pistols (along with musket balls) were made and Hook acquired one.
I don't remember Peter Pan specifically, but it would seem rather odd that Hook does not own a flintlock before he goes to Neverland initially. Flintlocks have been around since atleast the 16th century (in the LWM anyway), and cannons even before that. I'm pretty sure the Jolly Roger was equipped with cannons, and it would make sense that a pirate captain would have a flintlock pistol. Also, since JM Barrie fashioned Hook after many of the pirates that sailed the Spanish Main, a flintlock pistol would have been standard fair for the captain.
As for Hook not recognizing the gun in 2.11, That may have been more of not recognizing a modern pistol with it's more modern sophistication. The fact that he determined the purpose if it extremely quickly indicates (to me anyway) that he knew what guns were in general.
As I wrote this, I went and found a copy of PP on the internet and checked, and while it did not find HIM carrying a pistol, there was mention of one of his men (Starkey) holding a pistol. So, I would say that Hook knew exactly what a pistol was.
As a side note, in the original tale, it was Hook's right hand that was cut off, not his left (although most modern interpretations of PP have Captain Jas. Hook with his Left Hand removed).
Also, Oz is sorta advanced.Emerald City had skyscrapers and spotlights. And there was an old fashioned electric lamp along with some kind of machine (used to control Walsh's shadow, etc.) Behind the huge curtain in Walsh's room.