You can buy them at coin dealers and coin shows.
They are not rare.
Rare Coin Wholesalers was created in 1990.
Just the year does not make a coin rare.
No, they are not rare.
No.
It means that the coin is rare. For example a 1909-S VDB cent is a key date. This coin is rare.
Determine how many were minted, when and where and the numismatic grade and, last but not least, the availability of the coin for purchase
No and they will never be rare.
It does not have to be old at all. An error in the minting of a coin may make it rare. What may turn out to be a rare coin may have been minted in 2012, but nobody has found it and come forward with it yet.
vdb
No, it is not a very rare coin (as it is believed that 1,698. 000 of them were out in 1952). You can sell this with about $9 if the coin is in good state and with about $16 if the coin has never circulated.
The earliest the coin was produced by the US mint, the more rare it probably is. However, the mint state would also contribute to the coin's value.