The idea expressed in this statement is that the gopīs were comparing their attraction for Kṛṣṇa to an attack by demons; and to counteract their attraction for the beauty of Kṛṣṇa, they were also turning to Kṛṣṇa hopefully, because He is the killer of all kinds of demons. In other words they were perplexed because on one hand they were attracted by the beauty of Kṛṣṇa, and on the other they needed Kṛṣṇa to drive away the demon of such attraction.
This kaiśora age can be translated as adolescence. At the end of this period all the gopīs said, "Kṛṣṇa is the killer of the attraction of Cupid, and as such He disturbs the patience of all newly-married girls. Kṛṣṇa's bodily features have become so exquisite—it is as if they are all manifesting an artistic sense of the highest sort. His dancing eyes have dimmed the brilliance of the most expert dancer, and so there is no longer any comparison to the beauty of Kṛṣṇa." Learned scholars therefore describe the features of His body at this time as nava-yauvana, newly-invented youthfulness. At this stage of Kṛṣṇa's bodily features, the conjugal love affairs with the gopīs and similar pastimes become very prominent.
There are six features of conjugal love affairs, called peacemaking, picking a quarrel, going to meet one's lover, sitting together, separation and support. Lord Kṛṣṇa expanded an empire of these six features, of which He was the ruling prince. Somewhere He was picking quarrels with the young girls, somewhere He was scratching them with the nails of parrots, somewhere He was busy going to visit the gopīs, and somewhere He was negotiating through cowherd friends to take shelter of the gopīs.
Some of the gopīs addressed Him thusly: "My dear Kṛṣṇa, because of Your adolescent age, You have just become the spiritual master of these young girls, and You are teaching them to whisper among themselves. You are teaching them to offer solemn prayers, as well as training them to cheat their husbands and to join You in the gardens at night, without caring for the instructions of their superiors. You are enthusing them by the vibration of Your enchanting flute; and, as their teacher, You are teaching them all the intricacies of loving affairs."