Is it legal for my father to loan me a long gun registered under him for a day? I read 134-4 C "...may be leant to an adult for use within the State for a period not to exceed fifteen days..." What constitutes as an adult. I am 19 years of age. Sometimes my dad can't get to the range, any input. Was reading a little bit. Just was confused...

Thanks,
-Z

Adult = 18 or over.  Adult is the opposite of minor ... under 18.

Minors are allowed to possess long guns and pistols, too, as long as the minor complies with HRS 134-5.  Basically, if they are target shooting or hunting with a hunting license, a person 16 or older can possess a long gun.  If possessing a pistol while hunting, the pistol needs to conform to rules for hunting with such firearms. 

I think DLNR or the hunter's ed curriculum has a list of pistols and calibers that are legal to hunt with.

Minors under 16 in possession of a firearm while hunting or at the range have to be accompanies by an adult.

Is it legal for my father to loan me a long gun registered under him for a day?

Thanks,
-Z

Yes