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davidcyclebackCDVs can be dated to a time period due to the style, but rarely to a specific year without specific information. For example, a CDV with square corners almost always dates before 1870. while a CDV with rounded corners dates to later. Interestingly, 1860s CDVs are easy to date due to the distinct mount style, while later ones can be more difficult.
During the Civil War era, tax stamps were sometimes put on CDVs. These can date a CDV to a specific year just like with a cigarette pack.
There was a case where a collector had a CDV-style card that he felt was the first baseball card. I thought it indeed could be, the problem being it was impossible (as far as I saw) to date it to a specific year. The question wasn't so much if it was a baseball card, but what year it was made.
In the earliest years of cards, there are no clear answers. If you're sure of the year, you aren't sure if it's a real baseball card. If you're sure it's a real card, you can't be sure of its exact age. The Peck & Snyders are the first baseball cards I know of that are clearly baseball cards. I have seen few if any early CDVs or other items that are clearly baseball cards.
The topic of the origins of anything is confusing for a 51 year old, much less an 11 year old. Starting with this topic is like skipping algebra and starting with calculus II.