The rags-to-riches narrative for several idols is very common.
Jonghyun (Shinee) he came from a single, working mother home.
Yunho (DBSK) has mentioned poverty several times, right down to a time when he was even homeless in-between gigs trying to get $$ for his home (and remember, he was with SM in his teens...)
LeeTeuk (Super Junior) has mentioned his family was always in debt and strapped for cash, and he was/is responsible for their cash flow,
Actor (who even hosted music bank or inkigayo for a time before starring in a few really great roles), Park Bo-gum, has also mentioned his severe poverty state and abusive household - right down to even getting a restraining order against his father. The latest is pure
public mess between the father and son, and claims of PBG in a cult.
There are a lot more. The typical age for trainees are early to mid teens. Some like
GD - BIg Bang's frontman and ...forgetting her name,
Minzy formerly of 2EN1, Jessica (former girls generation)'s sister
Crystal in the now defunct (right?) fx, Taemin, Changmin, etc all started painfully early. If you look at their schedules, rarely are they allowed to go home (maybe 2x a year), and parental oversight is replaced by managers, whose paychecks are already tallied onto the trainees/talents - they're already knee-deep in debt and it only grows. Perks, (cars, houses, etc) are given to successful acts, but under the company name.
on the youth/ younger is better (so it would seem, esp looking at crotch-orientated choreographies by veteran groups like
Shinhwa), but they do push both beauties and "beasts" (to phrase it like JYP's description of 2pm....) The age range is referred to as the flower of youth, and you can find men referring to themselves like that.
finally.. I always thought Rain/Bi (another rags-to-riches story, where he never had enough to eat and he overworked his mother while he went out practicing dance....) was a high-priced gigolo & his handler was JYP. When Rain started getting international acclaim (asian first) JYP went everywhere with him. When you wanted raw footage (regardless if it was stepping down from a private jet or at a press conference), JYP spoke for him, and answered all questions addressed to Rain/Bi (bi which means rain in korean, btw). JYP treated rain like a muscle-ridden toy dog tucked under his arm.... and then Rain started wiggling his backside on command - everywhere, like it was cute!
For his "American Debut" coming over to Carson Daly's TRL in 2006/7, Carson asked rain to do a dance which he turned around and slowly swung his backside back and forth, as he looked over his shoulder, smiling in front of the camera - and that was it!!!
Apparently Rain is trying to show he's not an ajusshi (uncle/ title for an old"er" man - one step away from grandpa) by pushing his new album and look what he does here at 34:48
Obviously whatever he does with that backside is the key to his success.