This excellent answer to another question offers some statistics on median age of doctorate recipients from U.S. universities in 2009, across different disciplines.
However, we know that there is quite a bit of variation in PhD length internationally, as well as variation in the age at which students typically enter a doctoral program. So I would expect the age at doctorate to vary by country.
Is there any data available on median age at doctorate by field of study and by country?
NB: This is a reference-request question. As per the tag wiki excerpt, I am looking for answers that are backed up by a supporting document or citation (not opinions).