I like playing blackjack, I might go to a casino one day and try to win a lot of money.
I've played blackjack before.  It is also known as twenty-one. All the players compete against the dealer. 
How long has it been around for?
Good question.  I have no idea. But there are different ways of playing it around the world. In the U.S. the dealer is dealt two cards.  One up and one down. 
What are some other ways of playing it?
I don't know. Another type of gambling card game is community poker.  That where the cards are all dealt face up and placed in the center of the table. 
What is the oldest card game do you know?
Another good question that I can't answer. Card games vary by regions and cultures.