User blog comment:OneofthePendragon94/The age of Merlin, Arthur, Morgana and Gwen./@comment-85.227.173.194-20150510192720

I think that Morgana is older than Arthur. Some has pointed out that Uthers devotion to Arthurs mother makes is unlikely that he cheated on her because he is so honerable and loyal. However; it is at least as unhonerable and disloyal to sleep with a woman who is married (which Morganas mother was at the time). It also sounds as if Arthur wasn't born yet by the way Uther speaks of the matter.

The biggest reason why I believe Morgana is the fact that she says several times that she is the rightful heir to the throne. She believes that she is the heir to the throne ans bases all of her actions accordingly, therefore se must be older.