in 18. century
I don't think that there was Young Poland then. But in XIX and XX c. there were quite a few "Young Polands". There was "Young Poland" in literature, music, culture etc. in the end of XIXc. and begining of XX c. There was also political organisation "Young Poland" (Młoda Polska) established by emigrants (Poles) in Switzerland in 1834. This organisation was part of Mazzini's "Young Europe". The leader of that organisation was Karol Stolzman, partisan war theoretician. "Young Poles" took part in preparation to european revolution (future Europe Spring in 1846-8).