I have 800 cards dated between 2004 up to 2011.... Is it cool to to build a deck from a variety of sets? Trying to get into mtg and need a boost of knowledge.
You need to clarify what you mean by 'cool'. It is fun to use older cards, however, it is only allowed in some tournaments.
If you are going to play with friends (called "Casual Magic") then you should build decks with any cards you have. If your cards are too powerful, then your friends will complain. If your cards are too weak, then you might find yourself buying some new cards.