Board Thread:Questions and Answers/@comment-184.88.25.24-20131112235645/@comment-5674726-20141106195402

GianG wrote: I don't think the randomly changed the description from "young boy" to "young man", so he was certainly at least 2 and a hal years older than him. Anyway, Balinor straight from Camelot to Ealador after the end of the Great Purge, so 11 months (Great Purge) + travel from Camelot to Ealador (1 month?) + 9 months... Merlin is at least 21 months younger than Arthur, so all joins.

I assumed that Merlin is only 2 and a half years younger than Arthur, because I don't think Morgana is more of 2 years older than him.

Maybe if we work backwards.

The Great Dragon was captured exactly twenty years before the beginning of the series, so the oldest Merlin can possibly be in the first episode is 19 years and 3 months.

The journey from Camelot to Ealdor takes no more than a couple of days but Hunith and Balinor presumably didn't fall into bed together the day they met. I'd say that we can subtract at least a few months from Merlin's potential age to give his parents time to fall for one another, which brings us to 19.

Balinor said that he had a life in Ealdor, which would suggest to me that he was there for more than just a couple of months but, given that he was hunted by Uther and that he and Hunith never married, he wasn't there for an extended period.

Balancing the two factors, I'd say that Balinor was in Ealdor for no more than a year, which would mean that Merlin is at least a few months past his 18th birthday when he first appears, turned 21 not long after the end of Season Three, and was 22 in Season Four.

This would more or less fit with your first estimate.