孑然一身轻狂未改
[jié rán yī shēn qīng kuáng wèi găi]
Describing a lone person still holding onto his/her free-spirited and unrestrained nature. Although alone, they maintain their youthful exuberance and carefree attitude without having been tamed or changed by life experiences, thus giving off a vibe of individuality and perseverance.