Board Thread:General Discussion/@comment-27175367-20190508051927/@comment-37017073-20190520204117

I'm pretty sure Arthur's birthday is somewhere in autumn. It's been confirmed in commentaries and the like that his being sworn in as crown prince in Excalibur is his coming of age, so he's either turning or has just turned 21 at the time, and the episodes immediately following Excalibur both have to do with the harvest: Ealdor's in The Moment of Truth and Camelot's in The Labyrinth of Gedref.

His birthday being in the fall is also supported by the placement of The Wicked Day immediately following The Darkest Hour, during which Camelot had a feast celebrating Samhain. Traditionally, this was a festival marking the end of the harvest season and the beginning of winter and was usually celebrated from October 31st to November 1st, halfway between the autumn equinox and the winter solstice. The show appears to have stuck to this, as Alice Troughton refers to it as Camelot's equivalent of Halloween in the commentary for The Darkest Hour: Part 1.

Morgana's birthday is trickier, as the only time it's ever celebrated is in The Crystal Cave. The only clues that episode gives us are that the plants in the Valley of the Fallen Kings are full and green and the grass in the field that Merlin and Arthur walk through is very tall, which tends to give me the idea that her birthday is somewhere in late spring/early-to-mid summer. (Given the length of the grass, I tend to lean towards summer.)

As for her age, I tend to lean toward the view that she's older than Arthur, simply because it's the only way that her insistence that the throne is rightfully hers makes sense, though whether she's older by a few months (which is possible if her birthday is in spring/summer and his is in the fall) or by a year or two is open to interpretation.

Also, based on the fact that some of the last episodes of series 1 are concerned with the harvest and therefore presumably in the fall, I'd probably place the beginning of the show in early/mid spring, mostly because in Valiant it's still cold enough that the tournament spectators are all bundled up in cloaks and Morgana's wearing a fur collar and gloves. (Also, I can't picture Hunith sending Merlin off on a multi-day journey in winter, especially since he'd be traveling to Camelot on foot.)