The use of the term “father” for Christian mentors is quite ancient. Here is a quote from Clement of Alexandria that indicates this: “Words are the progeny of the soul. Hence we call those that instructed us fathers” (Stromateis 1.1.2-2.1).
Of course, Paul uses it thus in 1 Thessalonians 2:11. Our Lord emphasizes, though, that the term cannot be used in such a way that it compromises the fact that God the Father alone is our true Father. Any other father in Christ is relative compared to Him (Matthew 23:9).