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

Merlin:

Series 1: 18

Start of Series 5: 27

Arthur:

Series 1: 20-21

Start of Series 5: 29

Gwen: 

Series 1: 20

Start of Series 5: 29

Morgana:

Series 1: 23

Start of Series 5: 32 (Morgana will use the same illusion as Nimueh to make her look 20-25)

Gaius:

Series 1: 70

Start of Series 5: 79

Mordred:

Series 1: 10

Start of Series 5: 19

Alvarr:

Series 2: 28

Start of Series 5: 35 (sorry, I just had to include him! ;) )