GSoul has the most prolonged trainee period out among idols. However some idols have been in the industry for longer just due to how long their trainee period was. Most K-Pop idols go through long years of training periods before debuting in a K-Pop group.
Additionally KPOP training is great for getting in shape staying in shape developing body flexibility learning how to sing learning how to dance and finding an outlet for expressing yourself.
However its not uncommon for trainees to continue practicing and not get any sleep. 2AMs Jo Kwon has put up with 7 years training period while Super Juniors Kyuhyun debuted only after 3 months training period. However some idols have been in the industry for longer just due to how long their trainee period was. See the Kpop world has a concept called trainee debt that is not present in the.