What is the age and value of a 38 Colt Officer's Model target pistol serial 406805 N with a four inch barrel nickel plating ivory grips and engraving?

I would estimate it was made post WWII. The Sn range for 1943-1947 is 269000-50001. What it's worth depends on if it left the factory the way you describe it. I suggest you get it lettered by Colt. Go to their website for information on how to do this and price. You don't describe it in terms of Good, Very Good, Fine, Excellent or 90 95 percent, etc. Without that, there is no way to give a good estimate of worth, If it letters as factory nickel, ivory grips and engraving, you are looking at a price range of a thousand or so to multiple thousands, depedning on condition, accessories, box, manual. If it is not factory, and was done during the period, you could still be in the high hundreds to a few thousand or so. Again, it will depend on condition, etc.. If it was done say in the last 20-30 years, it will all depend on the condition of the plating, how good a job was done, who did the engraving, who did the ivory, etc.. In that case you would be in the couple of hundred to maybe a thousand or so price range.