I have been teaching English in South Korea for almost five years. I have met several native English teachers here who are over 50 years of age, some in their 60s. Most fit in quite well. With your experience, and if your health is good, you would be welcome by reputable schools here.
You may prefer small hakwons that have only one or two foreign teachers. Some directors of schools that teach adults told me they consider older teachers more reliable, but adult schools usually employ on split shifts morning and evening.
Hope this is helpful.