I am helping a friend to plan a trip in the Netherlands. He is 68 years old. Is there some discount on the train like in Belgium?
Not really, at least for NS (the main operator in the country). As far as I know, the only things seniors can get are
None of this seems relevant for visitors and, in fact, the info is apparently not even available in the English-language part of the website.
There are a few other train operators, mostly in the north and east of the country but I don't know about those.