I would disagree...I think that ageism is an issue since the older the female idols are they tend to get replaced by newer "fresher" options or alternatively they don't really want to be idols anymore and want to start a family or children or otehr ventures such as acting...
I disagree because male idols face the same problem: the one of being replaced by fresher faces, the only thing that makes it more 'easy' to have a longer career as a kpop idol is because fan-girls usually spend more money on idols buying merch, tickets and album. With that said, it this current generation, girl groups are being targeted to a female audience more and more so we will see if those groups are going to have a longer career