User blog comment:Morganamagic7/Siblings Age/@comment-5036924-20111216194144

I don't remember anything about the time of Morgana's birth, so maybe I missed that, but I always considered her a year or so older than Arthur. And she definitely didn't seem 16 to me at any point; in my head she was always in her 20s. :/

Plus I agree that to have any hope of claiming before Arthur she'd have to be older, though the fact that she was a) illegitimate and b) female already make her claim by right pretty shaky.