Please define "Normal operating condition for a vessel of it's age"
As a buyer, I would be concerned about a seller who would not agree to this. "What exactly are you hiding from me about this boat?"
"Normal operating condition" means,
1. It is not brand new and is not perfect;
2. Although it is aged, it does operate, it is not inoperable;
3. The operating condition is consistent with its age;
4. The seller does not know of any major material defect that would imminently impair its functioning.
Look at your marine survey - the marine surveyor gives an overall opinion of the boat's condition for its age. "Normal operating condition" would be "average" and functioning. That still allows for imperfections consistent with the age, or things that need to be addressed, but do not impair the functioning of the boat.
So a forty year old fiberglass boat with a twenty year old inboard engine is not perfect, but it works, and the boat would have the normal features of a forty year old fiberglass boat - faded, spider-cracked gel coat, oxidized metal coatings, aged standing rigging, etc. The twenty year old inboard might have a slowly leaking rear seal, lower compression, and/or burn some oil, but it still runs and the seller does not know of any defect (cracked block, water leaking into the oil, etc.) that would require immediate replacement.
It is certainly possible that a forty year old boat or a twenty year old engine could develop a problem that would prevent it from normal functioning the next day. This is not like a new home warranty, a new car warranty or a new boat warranty, the seller is not guaranteeing its operation for any particular period of time, just that it works now.
If you do not want to make any representations about the condition of your boat, that's fine. Sell it "as is" with no statements of fact about it, or sell it on eBay. The real problem is that sellers want to make all kinds of representations without any liability for the buyer's costs in reasonably relying on those representations. That may work with a sucker, but an informed buyer should not fall for that ploy.