Why is Les alarmed about today's younger generation?
The teacher is alarmed because the younger generation seemingly has no concept of God, eternity, or spiritual things. They live for the here and now and for the gratification of the flesh, with no spiritual understanding, and this frightens him.
Les explains that he is alarmed about today's younger generation, "our kids," because they seemingly have no concept tonight of God, or of eternity, or of things spiritual. They are living for the here and the now, and for the gratification of the flesh, with no concept. He says it is scary and that it just scares him to death. This concern comes in the context of Peter's warning that since all these things will be dissolved, we ought to be holy and godly, and Les connects it to the foolishness of rejecting or attempting to thwart such a God.