There is no age discount for elderly people when it comes to train travel in the Netherlands. To qualify for a discount, they need to get and pay for a season ticket.
You could get a bit of discount if you travel during off-peak hours by buying a ticket in advance, though. You can read more about that on this page. Don't buy it way in advance, since bought tickets cannot be refunded.
Also, note that there is no train station in Hoek van Holland, and Leopoldsburg is not in the Netherlands, but in Belgium. This complicates things ticket-wise, since you not only need a domestic train ticket, but also one for the metro from and to Hoek van Holland, and one for international travel.
You can't take your bike on the RET metro on weekdays before 09.00 and between 16.00 and 18.30. https://www.ret.nl/en/vraag-antwoord/de-reis/reisinformatie/algemeen-reisinformatie/can-i-take-my-bicycle-onto-the-bus-tram-metro-or-fast-ferry.html
You have to change at Schiedam Centrum for an NS to Rotterdam Centraal. Of coninue on the metro to Eendrachtsplein and walk/cycle from there to Rotterdam Centraal.
More information on booking a ticket for your bike from Schiedam Centrum to Leopoldsburg (you can take your bicycle on the Intercity Brussel: https://www.nsinternational.com/en/before-you-go/taking-your-bicycle-with-you#Taking_your_bicycle_on_board_I_(Transporting_bicycles_on_train)-anchor
Returning from Arnhem to Hoek van Holland I would recommend changing between train and metro ar Rotterdam Alexander. You need to buy domestic bicycle ticket online: https://www.ns.nl/producten/en/toeslagen/p/fietskaart-dal Peak time restrictions apply.
RET doesn't charge for taking your bicycle on the metro, as long as you travel outside peak times.
A good page with tips for travelling via Harwich and Hoek van Holland is: https://www.seat61.com/trains-and-routes/london-to-amsterdam-by-ferry.htm
Thank you everyone for your really helpful replies. I have decided to cycle the 18 miles from Hoek Van Holland Haven to Rotterdam Centraal and get an IC train from there to Leopoldsburg. In the UK, we have an App (TrainLine) which can be used for purchasing tickets for International rail travel.
In addition to my journey in September 2024, I hope also to visit NL in the Spring 2024 to cycle LF Maasroute. I shall get an IC train from Rotterdam Centraal to Maastricht and cycle back towards Rotterdam / Hoek Van Holland Haven from there. I look forward to both trips.
Best wishes to all! Bill Evans
Thank you everyone for your really helpful replies. I have decided to cycle the 18 miles from Hoek Van Holland Haven to Rotterdam Centraal and get an IC train from there to Leopoldsburg. In the UK, we have an App (TrainLine) which can be used for purchasing tickets for International rail travel.
Trainline seems to book these international through Belgian railways, since they're always €1 more expensive than booking via NS. In addition, it will probably be cheaper to split this ticket in Noorderkempen, since Belgian railways have a quite cheap senior ticket.for domestic journeys.