How middle aged are we talking here? I'm in my forties and really enjoying my training here in Bangkok. There are a few of us older people and the trainers are great with not pushing us beyond what we're comfortable with.
I dunno about 3 years from now, but I left the country and came back, (before my 180 days were up), and nobody asked me any questions about renewing my muay thai course.
You should use the search option here, but I got mine through Tiger Eye based on recommendations from this group. Great training and price, plus really professional.
For Muay Thai I got mine from Tiger Eye in Bangkok. They were recommended by a few people in the group and rightfully so, very helpful and professional. Been meaning to make a post about it.