St. Thomas claims that the wisdom of philosophy and theology takes a great deal of time to learn, because wisdom cannot be learned until the passions of youth have cooled down. Since St. Thomas elsewhere likens the passions of youth to drunkenness, it makes sense to say that the wise man must be sober mined.
Perhaps one of the dangers in learning philosophy too young is just this lack of sobriety. The young or the young-at-heart who have some skill at philosophy and theology can easily fall into looking to it to provide wild flights of ecstasy and/or to provide them with a sort of club that they can swing at interlocutors to release youthful aggressions. This sort of youthful drunken energy can be a good thing, so long as the energy is being channeled and led by sober minded wise men, but the atmosphere and ideology of the modern college makes it inevitable that philosophy and theology would become equal parts artistic-metaphor-flights-of fancy and cudgel-to-beat-guys up.