How do you prove you have been celibate for 3 years?
If a person cannot be relied upon to confess the truth and make pledges and receive vows honestly, with candor and truthfulness, then they certainly are not qualified for the Priesthood.
If they have a problem responding to that question, they don't belong there, otherwise.
People should be asking here why anyone who WASN'T chaste and celibate in the years prior to the seminary would even be seeking the Priesthood as a profession. Therein lies the truth of the matter, why people who refuse or feel they are not able to be productive and thrive as celibate and chaste are even trying to enter the Priesthood, much moreso remain there.