noun
A somewhat old-fashioned or literary word for a particular time, period, or era. Often used in set phrases like その頃おい (at that time) or 若い頃おい (in one's younger days).
その頃おいは、まだ学生でした。
At that time, I was still a student.
若い頃おいの思い出を語る。
He talks about memories of his younger days.
頃 (ころ) is a common suffix meaning 'around the time of' or 'approximately', while 頃おい (ころおい) is a standalone noun meaning a specific time or period, and has a more literary feel.
時代 (じだい) is the standard word for 'era' or 'period', used in both formal and everyday contexts. 頃おい is more limited to personal or nostalgic time references.
Derived from 頃 (ころ, 'time') + おい (an old suffix possibly related to 生い 'growth' or 追い 'pursuit', but the exact derivation is uncertain). The word is now considered somewhat archaic.