My wife was offered a couple of posts in Vietnam when she was 49.
I have no experience of South East Asia, but was offered posts in Japan when I was 55. When I went to China at 56, one of my collleagues was 61.
I look through the the jobs on offer at tefl.com occasionally and note that some countries/institutions won't accept applications from people over 55, but I don't imagine that you'll have any problems at 45. The reason there are so many younger people in TEFL is the lack of well-paid jobs or stability, not prejudice against age, in my opinion.