Today's list is as follows:
Jean-Claude Juncker (born 1954), Prime Minister of Luxembourg since 20 January 1995 (EPP)
José Luis Rodríguez Zapatero (born 1960) Prime Minister of Spain since 17 April 2004 (PES)
Lawrence Gonzi (born 1953) Prime Minister of Malta since 1 May 2004 (EPP)
José Manuel Barroso (Portuguese, born 1956) President of the European Commission since 23 November 2004 (EPP)
Andrus Ansip (born 1956) Prime Minister of Estonia since 12 April 2005 (ELDR)
Angela Merkel (born 1954) Chancellor of Germany since 22 November 2005 (EPP)
Fredrik Reinfeldt (born 1965) Prime Minister of Sweden since 6 October 2006 (EPP)
Traian Băsescu (born 1951) President of Romania (which joined EU on 1 January 2007) since 20 December 2004 (EPP)
Nicolas Sarkozy (born 1955) President of France since 16 May 2007 (EPP)
Donald Tusk (born 1957) Prime Minister of Poland since 16 November 2007 (EPP)
Dimitris Christofias (born 1946) President of [Greek] Cyprus since 28 February 2008 (PEL)
Borut Pahor (born 1963) Prime Minister of Slovenia since 21 November 2008 (PES)
Werner Faymann (born 1960) Chancellor of Austria since 02 December 2008 (PES)
Valdis Dombrovskis (born 1971) Prime Minister of Latvia since 12 March 2009 (EPP)
Jerzy Buzek (Polish, born 1940) President of the European Parliament since 14 July 2009 (EPP)
Dalia Grybauskaitė (born 1956) President of Lithuania since 12 July 2009 (EPP)
Boyko Borisov (born 1959) Prime Minister of Bulgaria since 27 July 2009 (EPP)
Herman van Rompuy (Belgian, born 1947) President of the European Council since 01 December 2009 (EPP)
David Cameron (born 1966) Prime Minister of United Kingdom since 11 May 2010 (ECR)
Viktor Orbán (born 1963) Prime Minister of Hungary since 29 May 2010 (EPP) - previously PM 1998-2002, before Hungary joined the EU
Iveta Radičová (born 1956) Prime Minister of Slovakia since 8 July 2010 (ECR)
Petr Nečas (born 1964) Prime Minister of the Czech Republic since 13 July 2010 (EPP)
Mark Rutte (born 1967) Prime Minister of the Netherlands since 14 October 2010 (ELDR)
Enda Kenny (born 1951) Taoiseach since 09 March 2011 (EPP)
Pedro Passos Coelho (born 1964) Prime Minister of Portugal since 21 June 2011 (EPP)
Jyrki Katainen (born 1971) Prime Minister of Finland since 22 June 2011 (EPP)
Helle Thorning-Schmidt (born 1966) Prime Minister of Denmark since 3 October 2011 (PES)
Lucas Papademos (born 1947) Prime Minister of Greece since 11 November 2011 (Ind)
Mario Monti (born 1943) Prime Minster of Italy since 16 November 2011 (Ind)
Elio Di Rupo (born 1951) Prime Minister of Belgium since 06 December 2011 (PES)
Jadranka Kosor (born 1953) Prime Minister of Croatia (which will join EU on 1 July 2013) since 6 July 2009 (EPP)
There have been four changes since the June 2011 summit (Denmark, Greece, Italy, and at long last Belgium), with Zapatero, Pahor, Radičová and Kosor all on borrowed time thanks to recent elections in Spain, Slovenia and Croatia and imminent elections in Slovakia. This is also Buzek's last appearance as his term comes to an end in January.
The EPP have lost Italy and Belgium but gained Croatia (whose leaders will sit in all EU council meetings from now on, even though they don't actually join for another year and a half) for a total of 16 of 28 heads of state and government plus the presidents of all three EU institutions. The PES have lost Greece but gained Denmark and Belgium, putting them on 5; the Liberals lose Denmark and go down to level pegging with the ECR on 2 each; the others are 1 Communist and 2 Independents.
There are five women, the German Chancellor, the Lithuanian President, and the Prime Ministers of Denmark, Slovakia and Croatia (the last two of these being on borrowed time).
On average they have been in office for 3 years and 5 months, Dalia Grybauskaitė being more or less exactly on the average as well as median points of the leaders of EU27 (if you include the other four, she is still on the median but Kosor, who took office the previous week, is closer to the average).
I make the average year of birth 1957, but the median 1956 (the birth year of Grybauskaitė, Barroso, Ansip and Radičová). Buzek is the oldest; Van Rompuy is older than any national leaders except Monti and Christofias.
I am still younger than all of them except the Latvian and Finnish prime ministers. The Danish prime minster's husband was two years below me at Cambridge, but she is a bit older than I am.