Big Daddy, The simple anwser is yes to carrying a handgun under 21 while hunting. Here are the RCW numbers that explain it completely.
9.41.040
9.41.042
9.41.050
9.41.060
The main law (rcw 9.41.240) states this. Unless an exception under RCW 9.41.042, 9.41.050, or 9.41.060 applies, a person at least eighteen years of age, but less than twenty-one years of age, may possess a pistol only:
(1) In the person's place of abode;
(2) At the person's fixed place of business; or
(3) On real property under his or her control.
The one big thing about being under 21 when handgun hunting is no store I have ever been in will sell you ammo if it will fit a handgun. Then you also have to beware of cops who have wild pig hairs up the rump and stop someone. They tend to get excited about handguns on people.