This information might be a little out of date, but years ago I was working at a Hogwan in South Korea and part of my responsibilities was dealing with applicants, in consultation with the Korean director. I can tell you that my director and his brother were both very hesitant about older applicants, mainly because they considered it very strange that someone of that age would want to come to South Korea and become an entry level teacher. I believe this was a culture issue rather than their personal quirk. Some occupations in South Korea just seem to be designated primarily for young people, and there also seems to be a certain age range when you should be traveling abroad to seek you fortune. That being said, my director was still willing to consider older applicants, and at the time there didn’t seem to be restrictions on work visas for teachers who were over 55. It is my impression that the stigma about older teachers wasn't as heavy for university positions, especially if you want to teach content courses rather than being a conversation instructor. At least, I knew some older instructors in those positions.