Who was the fourteen year old boy and the old man in the forest in Excalibur, from The Tales of King Arthur?

I believe that the fourteen-year-old boy and the old man was Merlin. Merlin was a wizard and he had an encounter with Arthur in the forest and disguised himself as a fourteen-year-old boy telling him that he is Uther's son by Igrayne. Arthur didn't believe Merlin because of his young disguise so Merlin left and returned as an old man.