Publish the age of your component when selling (let's discuss)

I've noticed that many sellers don't publish the age of the item or items they are selling on Audiogon.  I believe it should be required that the age or original manufacturing date of the item being sold be clearly stated.  Some do but many don't.  Sometimes you can see the manufacturing date on the back of an item should the seller post a photo clear enough to see it but a prospective buyer shouldn't have to find it out that way.. What is the fear here?  This is especially important when it comes to sources such as DVD and CD players.  No matter how great the CD player may have been at the time, an 8-10 year old unit (let's face it) is worn and the DACs are no longer state of the art. You may think you have a piece of gold but the transports wear and again the DACs are antiquated. 

Opinion now:
I believe that many of the CD players on sale now that are say at least 10 years old are over priced.  To back up what I'm stating here, out of sheer curiosity and with a little extra cash I had, I very recently bought a brand new Onkyo C-7030 CD player for $200.00.  Got it home and in a matter of a few days, OMG, the overall sonic fidelity and extreme detail is produces when playing decently recorded CDs is nothing short of amazing.  Why would I purchase a pre-owned $1,000.00 player when this Onkyo sounds just as great?  I know this is a loaded question and may not be too popular but would love to hear what the members think.  No offense to anyone's machines.  THANKS.  
Wow excellent discussion.  Love it. Balanced and fair input and great suggestions.  Elizabeth, thanks for the great Google suggestion.  That is surely one way to find out.  One comment:  if you are the original owner, you would (or should) keep the original box and receipt.  Then when you go to sell the item, you can refer to the receipt and date.  That's a practice I follow.  For non-original owners, a little more difficult but certainly discoverable.  I just feel that the seller could expend a little more time to research this information for the buyer.  That's all.    
You can always try to contact the manufacturer with the serial numbers. Most are willing to give you a ball park figure.
A good reason to know the manufacture date is the updating that manufacturers do over time to their gear without changing model designations.  Vandersteen Audio is famous for this as RV's designs are never final.  As he does R&D for potential new products RV may find a crossover component, for example, that performs more admirably than what he has been using.  When that happens he will often incorporate that improved part into other speakers in his line.  

One of the biggest examples of his is the use of carbon tweeters.  Once he perfected the design and perhaps more importantly, the manufacturing for those tweeters, they began to trickle down the line.

I recently discussed this very issue with Steve McCormack.  He told me that very little in my 20 year old modded DNA-1 would be still in the amp. when I receive it from the rebuild he is currently doing on it.  Not because what he did two decades ago wasn't valid at the time, but because so much has been learned and so many parts have improved over that span of time as he has worked on many different amplifier designs.  The "vintage" of your kit matters!