User blog comment:Emily Windsnap/How old are the Merlin characters?/@comment-4190137-20120504080114/@comment-5102537-20140430104951

Lurker wrote:

"The only thing with this is other than between season 2 n 3, 4 n 5, we don't know how many years was skipped. A the beginning of Season 4 someone makes a comment about Uther being the way he was for months. If it has been a year why not say it. Im not saying all this is wrong, but I'm thinking they are all about a year or two younger than what we think."

I guess we will never how old the characters really were. However, Uther told Gaius that Vivian grew lonely, not he himself. And given that he told Kathrina/the troll that he hadn't been with another woman ever since Igraine, and if this was the truth, Morgana has to be older than Arthur. Moreover, Katie McGrath once said that Morgana was older than Arthur. It has never been directly confirmed on the show though.

As for the time gap between seasons three and four, Gwen said to Gaius that "it's been a year since Morgana betrayed him", referring to Uther's condition.