A millennials railcard goes on sale on Tuesday, but only 10,000 will be available and they are unlikely to save regular commuters money.
Britons aged 26-30 will be able to buy the discount card on a first come first served basis, the Rail Delivery Group (RDG) said.
There will be a limit on the number of 26-30 Railcards available while the scheme is trialled to assess the impact on revenue and passenger numbers.
It will cost £30 each year and save passengers a third off most fares.
The card is aimed at leisure travellers, with no discounts on season tickets and a £12 minimum fare on all journeys between 4.30am and 10am, excluding weekends and public holidays.
It must be bought online and downloaded onto a smartphone.
The card was previously only available to a limited number of people in East Anglia.
Chancellor Philip Hammond said in his Budget speech in November that the railcards would give "4.5 million more young people a third off their rail fares".
The RDG, which represents train companies and Network Rail, was unable to provide an exact time for when it will go on general sale, but confirmed it will be at some point on Tuesday morning.
There was previously no nationwide railcard available for people travelling alone between the ages of 26 and 59 unless they were disabled or in the armed forces.
An RDG spokesman said: "The trial of the 26-30 Railcard is part of the rail industry's long-term plan to change, improve and boost communities by enabling more people to travel by train.
"Research being gathered as part of the 26-30 Railcard trial is being used to inform discussions with the Government about a national roll-out, and to develop new products that make leisure travel easier and better value for customers."
The number of train journeys made in the three months to the end of 2017 fell by 0.9% year-on-year, according to the Office of Rail and Road.
This was driven by an 8.1% fall in season ticket usage.
Passengers were hit with the largest annual fare rise in five years on January 2, with average ticket prices across Britain increasing by 3.4%.