D8: Unable to set cache max-age on ResourceResponse
The referenced question from 4k4 describes how to disable the internal page cache completely. 

To not disable but set an expiration on the anonymous/internal page cache, you can use the Expires header, just set it to a date in the future and that will be respected. That's the only thing that the internal page cache module currently respects.

See the linked core issue for more information, it's partially simply an overlook that it wasn't done before 8.0 but now it would be an API change to start respecting it and lots of things would then make Drupal uncacheable, like the language switcher block. So we'll have to be very careful with any change we make.