Juvenile felonies in the State of Washington DO result in the loss of your state and federal rights to own or possess fire arms. It is a permanent loss only recoverable after the statutory waiting period [ varies with the type and class of the original felony], by going back to the Court in which you were convicted and sentenced [called a Disposition in Juvenile Court], and petitioning the Court to restore your rights. It is not automatic and is not "included" in having your Juvenile Record Sealed at age 23 [earliest you can do that unless it was a successful Deferred Disposition].
So unless you have had a hearing in the Court [County Jurisdiction] that originally convicted you and had your rights specifically re-instated [ In which case you would have gotten a copy of the Court Order].... you are still prohibited from owning or possessing [including constructive possession] any fire arm.
Hope you get it figured out... remember it's one thing to be the oldest kid in Juvenile Detention....Quite another to be the youngest kid in State Prison.