Likely a modern variant of Kirsten or Karsten
Kestin is a rare name with ambiguous roots, most likely emerging as a modern phonetic variant of the Scandinavian Karsten or the Scottish Kirsten. In some contexts, it is associated with the Germanic name Christian, meaning 'follower of Christ'. Its usage in the United States is contemporary and quite rare.
Less common today
Kestin isn't in the latest US Top 1000. It last peaked at #8,604 in 2011.
US births per 5-year period, 1990βpresent (SSA data).