RCW 9A.040.080 gives the statutes of limitations for various criminal offenses. Assuming you're talking about sexual abuse that amounts to rape of a child, child molestation or indecent liberties, the statute allows for prosecution until the victim's 28th birthday.
However, just because the perpetrator cannot be prosecuted for abusing you does not mean that you can't/shouldn't report the abuse to law enforcement, especially if he/she still has contact with children.
I'm sure that this goes without saying but I'd also recommend seeking counseling. There is counseling specifically tailored for adult victims of child sexual assault.