Excerpt of a lecture given by HH Bhakti Rasamrita Swami at the Sannyasa Candidate Training Seminar in Mayapura (February, 2012).
There is a verse in the Puranas that states that sannyasa is forbidden in Kali-yuga:
kalau parca vivarjayet
[Cc. Adi 17.164]
In this age of Kali, five things should be avoided: one is performing sacrifice by offering cows; performing sacrifice by offering horse; and oblation offering to the forefather