One relatively easy (and quick) way to see how old your comic books are is to check out the date on the cover. It's not perfect, but it will give you a general idea on the age of the book.
Golden Age (1930s - 1950s) = 10 cents
Silver Age (1960s) = 12 cents & 15 cents
Bronze Age (1970s) = 20 cents, 25 cents, 30 cents
Copper Age (1980s) = 60 cents, 75 cents, $1.00
Modern (1990s and later) = $1.00, over a dollar
Again, this is just a rough guide—and an excuse to enjoy some cool comic book covers! Most new comic books won't ever be worth a ton of money, but some will!
My personal favorites of all are the Marvel "20 cent" covers. I just love the combination of "teaser" words at the bottom with the beautiful illustrations.