I'd like to study fashion design/bachelor degree at age 30!Is that crazy?

I does not appear you're crazy at all! If you've worked somewhere for 20 years, 30 years or 50 years, has nothing to terminate. It takes several years before one can feel your instincts about it is the right profession for you. I think the fashion industry is a convenient job that profession, but I would not prefer to be somewhat in the fashion industry in South Korea. I would be in America, or Similar, where it is a little more marketing, then you can serve better.