Why not just change to an 18-30 Railcard instead of 18-25 and 26-30? Or do they have different T & C's?
It's actually
16-25, as otherwise 16 and 17 year olds would face a doubling in their fare (vs being 15), instead of the 'mere' 32% increase they face if they have a Railcard!
And yes, I do suspect that eventually the 16-25 and 26-30 Railcards will be changed over to one product; that being said, one obstacle may be that the 16-25 Railcard is actually available to someone of any age, if they are a higher education student, whereas the 26-30 Railcard is strictly for that age range. The 26-30 Railcard also does not have the July and August exemption from the £12 pre-10am minimum fare on walk-up tickets. Also, holding a 16-25 Railcard is sometimes used as eligibility of a student discount for certain TOCs, e.g. TPE.