When he was a senior in high school, Lim joined the theater group called Kwangto, an acronym of Kwangdae Tokkaebi referring to traditional performers and hobgoblins in Korean, where he was first introduced to theatrical performance. Lim then played the role of the pastor in The Good Doctor by Neil Simon and won the prize of best performance in the Fourth Youth Theater Festival in 2000. He also directed the play, Pay Tuition Back, at the school festival. He continues to maintain a good friendship with fellow actor Shin Dong-wook, whom he met at the time.