http://french.about.com/od/vocabulary/a/an-annee-jour-journee-matin-matinee-soir-soiree.htm Here's a good explanation.
I thought of about five different possible english ways to say this and tried "A century lasts one hundred years" which, as it happened, was not in the list of correct translations. They can't list them all but I agree that "A century maks a hundred years" is simply wrong in english.
Use "années" when you wish to emphasize the duration of those 100 years, rather than simply how many there are. I don't think we have this concept in English. The following is a great explanation of this and similar duration words: