Usually peaches drop leaves near or soon after first frost. The more vigorous the tree the later. If really water stressed leaf fall will be sooner. Less nitrogen which usually equates to less vigor and the leaves may fall sooner.

Your young tree is moderately vigorous and should drop it's leaves soon after first frost. A long stretch of cool cloudy weather without a freeze will also promote leaf drop. Trees in my greenhouse where it never freezes drop leaves in Dec.