The GRO's searchable online index is capped at 1957. From the GRO's FAQ page:
Q6. Why aren’t death records shown up until 1965 rather than 1957?
Death records have been digitised up to 1957 but not beyond at this stage.
Q7. Are there any plans to add further to the records shown in the index i.e. add in marriage indexes and further historic death data?
Completing the digitisation of records would require significant investment and there are no current plans to resume this work but we continue to monitor the scope for future opportunities to complete the digitisation of all birth, death and marriage records.
So at present 1957 is a hard limit due to record digitisation, and that probably won't change any time soon.
(I'd expect that this will be reviewed after the current PDF pilot ends, but it will probably be at least months before any conclusions are published, and there's no guarantee that the situation will change.)
That doesn't appear to stop you from ordering a certificate from after 1957, though. If you can find the GRO index reference from another source, you can order a paper certificate in the usual way. Otherwise, you can get them to search for it. From the same FAQ:
If you are unable to trace or do not have the index reference you may still apply online for any event which took place on or after 1st July 1837 to 6 months from the current date (for marriages this period is extended to 18 months) provided you have sufficient information to identify the entry. A 3 year search for the index reference will be carried out. You should supply the exact date of event if you have it. If you don't have the exact date, enter 01/01/YYYY and we will search the specified year and one year either side. If you do not provide an index reference number, your application will take up to 15 working days to process. There is a separate policy for events which have taken place in the last 50 years and full identifying information must be provided (see Q7 under “Important information on delivery times and policies.”)
As 1959 is outside the 50-year limit, you should be able to have the search done as described if you don't know the reference. But this is for a paper certificate only, at full cost, and will take longer.