This is an excellent development because FreeBMD has limited coverage of death registrations after 1983.
For clarification, this now means the Official GRO Online Index web site https://www.gro.gov.uk/gro/content/certificates/indexes_search.asp now has Civil Registration death records as follows:
- 1837-1957 records include age at death
- 1984-2019 records include year of birth.
For the period between 1957 and 1984 you should use FreeBMD https://www.freebmd.org.uk/ who have transcribed the original GRO index books. The index books contained the following information for deaths:
- 1837-1865 no record of age at death
- 1866 to Mar 1969 includes age at death
- from 1 Apr 1969 includes exact date of birth
The pay sites also have their versions of the GRO index covering the whole period from 1837 to around 2008 but the transcription quality is not as good as FreeBMD. FamilySearch uses the version from Findmypast. I would only cite these as a source when they provide evidence that cannot be found in the matching record in the GRO online index or FreeBMD.