这句中的引文用了比喻来说明过早接触哲学的坏处。如果过早，就容易把哲学当成辩论的工具，四处招惹。

They have now reached the age of thirty; it would not have been wise to let them "taste the dear delight too early; … for you men, when they first get the taste of philosophy in their mouths, argue for amusement, and are always contradicting and refuting, … like puppy-dogs who delight to tear and pull at all who come near them"(539).
他们如今已年届三十，倘若让他们“过早品尝那份珍贵的乐趣实属不明智；……因为你们这些人，一旦初尝哲学的滋味，就为了取乐而争辩，总在反驳、总在驳斥……就像小狗崽，无论是谁靠近，都喜欢去撕扯（第539节）。

所在段落

The Story of Philosophy《哲学的故事》第1章Plato第7节VI. The Psychological Solution第13段第2句：

They are taught philosophy. They have now reached the age of thirty; it would not have been wise to let them "taste the dear delight too early; … for you men, when they first get the taste of philosophy in their mouths, argue for amusement, and are always contradicting and refuting, … like puppy-dogs who delight to tear and pull at all who come near them"(539). This dear delight, philosophy, means two things chiefly: to think clearly, which is metaphysics; and to rule wisely, which is politics. First then, our youngElite must learn to think clearly. For that purpose they shall study the doctrine of Ideas.
浙江大学译本：他们被教授哲学。如今他们虽已三十岁，让他们“过早品味这珍贵的趣味实属不明智……因为年轻人初尝哲学定会为了趣味而争论，时时要反驳诘难……就像幼犬，不论是谁接近它，都喜欢去撕扯、去拉拽”（第539节）。

上句见：Day406