Tā / huí / gù / guò / qù / shí / gǎn / tàn / zì / jǐ / nián / qīng / shí / bái / huó / le / hěn / duō / nián。

他回顾过去时感叹自己年轻时白活了很多年。

Looking back on the past, he lamented that he had wasted many years of his youth.