We're wanting to venture out from our normal campgrounds on the West Coast.

I've heard about the ten year rule for years on this site. Okay technically years on the old RV.net site but it's still the same to me. First off I think the ten year rule is not very common until you get into the really fancy (expensive) parks. If you are staying in state parks, national parks, county parks city parks etc you're not going to have that rule. A private park may have that 10 year rule. But I think most of those are one of those rules to have on the books just in case they need it. Like when you roll up in a falling apart dilapidated RV. If  your coach is in good condition visually I think most will turn a blind eye to it.

Ours is right at ten years.  Haven't had a problem.  

I have not heard of that rule being strictly enforced.  It is mostly a way for parks to exclude junk rigs held together with duct tape and covered in rust.  An older rig in good clean condition and well maintained should not have any issues.