How old was Merlin when first came to cAMELOT?

This is all a guess.

• Merlin is 15 (He was born during the Great Purge; Hunith and Balinor were still in Camelot trying to avoid Uther; and for a time they did and settled in Ealdor.)

• Arthur is 20 (His birth resulted in the Great Purge which ended 20 years earlier and he turns 21 in Excalibur 1x09)

• Morgana is 21 in the show's beginning (She is older than Arthur)

• Gwen is 18 (She looked older because she had a rough life)