Ageism has been an issue in Thailand for a while and it's not going away, sadly. It's even worse for Thais. Just go on any Thai jobsite and try and find jobs for anyone over 35. It's similar for us foreigners too, but the 'age limits' vary and aren't nearly as downright nasty as they are for Thai nationals.
I'm 50 now, have an education degree and twenty years' teaching experience. However, I can't get a 'top job' anymore, despite excellent references and experience. Recently, I applied for a job paying 70,000 up. It stated that you must have an education degree/QTS etc. I applied and they didn't even reply to my email. However, they did reply and offer a job (at 85,000 a month) to a young handsome chap I know with no B.Ed or QTS. Fair play to him for applying without credentials deemed 'essential' in their advertisement.
There was no 'age limit' mentioned in the ad, but obviously there was. There was no other reason to reject my application out of hand (they just asked for Certs, CV and a photo to be sent). And yes, I know how to write a good CV.
I'm happy for the chap. Good luck to him. But it has made me realise that I need to look at going back home to teach there. In Thailand, it's all down to private schools wanting pretty young faces representing their schools on the website, on the billboards and just for the parents to swoon over. Young, fresh-faced teachers help to sell the schools here. And money is important to those running some of these rackets, I mean schools.
I'm still getting some good offers, but not at the level I'm used to. And it's only going to get worse as I get older. I've now realised that you can't help feeling angry and frustrated at times due to the rampant ageism here, but that you need to just let it go. They aren't going to change. Cash is king.