How does Mr. Lang represent the archetype of the sage or the mentor?

He guides Kieran and offers advice based on his experience.

An archetype is a character, action, or situation that shows a universal pattern of human life. The sage or mentor archetype is an old and wise character, who guides the hero of the story in the right direction. In this passage, Mr. Lang is Kieran's trainer, who guides Kieran and gives him advice based on his experience as a gymnast.