I don't think it will bother most readers on this board so much, becasue most foreigners don't visit this place anyway.
I don't know whether K-Place have Age Discrimination intentionally or not, but some people may find it offensive becasue their price range is so wide, i.e. 400 baht for customers older than 49 y/o but only 99 baht for 49 y/o and younger.
This different-price-for-differnt-age admission fee is not really uncommon in farangland either. Several saunas in Europe, the US and Canada offer cheaper admission fee if you are younger than 25 for example. Anyone who is 25 yo probably wonders why he has to pay $18 when another person who is 24.5 yo pays only $12 !.
Most saunas in the UK avoid mentioning "age" but offer discount for "students" to attract younger crowds. So when I did a master degree at 30, I was entiled for a discount too.
Several saunas ( especially the smaller ones ) in London offer discount not only for students but also for senior citizens. I haven't heard the senior citizens complain anything then.