User blog comment:OneofthePendragon94/The age of Merlin, Arthur, Morgana and Gwen./@comment-5505930-20121114173130/@comment-5822565-20121114182448

11 years i think

gaps:

series 1 -   series 2  ,,,, 1 year

series 2 -  series 3  ,,,,, 1 year

series 3 - series 4   ,,,,, 1 year

series 4 - series 5 ,,,,, 3 years

total = 6 years in the gaps

now, presuming each series lasts about a year in their lives, that makes 11

explaining the fact that mordred has gone from around the age of 10-12 to now being about 20-22