I disagree, first because I don't think +Gregory is saying that. Second, I don't think Moses or Paul or Theotokos grew up planning to become "professional saints," Kolo mou. They were called to holiness and submitted in due time, realizing that it was God who appoints "apostle, prophets, teaches..." and siants in the Church, and set them apart from all eternity, and not their ego or pride.
This is what the Holy Father means when he invites other to become saints; it has nothing to do with becoming a "professional saint", whatever that is. Saint = one who is holy ("sanctus"). It is not an office in the Church or any special recognition. Indeed, most saints are known only by God. Which is why we have the Feast of All Saints.