Reforms to reduce degree times have not yet cut down on numbers of so-called "Dauerstudenten" - eternal students who can take up to six years for their undergraduate degree before embarking on a lengthy master's course.
Under the old German system, students were allowed to take semesters off to work, earn cash, travel, do work experience placements or study abroad. This led to lengthy degrees which could take years to complete.
At its outset in 1999, the EU's Bologna Process aimed to harmonize university education across member states.
Germany was particularly keen to shake off its reputation for having the continent's oldest graduates - on average 28 years old.
But the reforms sparked protests in Germany from students who said switching to British-style three-year bachelor's and a separate master's would restrict the flexibility and depth of study they were used to.
Three-quarters of Germany's 2.4 million undergraduates have now switched to the British six-semester bachelor's, usually designed to be completed over a maximum of three years.
Supporters of the Bologna reforms said they would revitalize German higher education. But new figures suggest the average study time for a bachelor's is still around four years, wrote the Frankfurter Allgemeine am Sonntag (FAS).
In North Rhine-Westphalia, where around a quarter of German students are based, the average student last year took 8.64 semesters or just over four years to graduate.
In Bavaria, students took an average of eight semesters and in the capital Berlin they needed 7.8 semesters, the leaked government figures showed. Official government statistics for 2013 are due to be released at the end of September.
The latest government statistics showed German master's students were now on average just over 29 years old at the point of graduation.
One recent graduate told The Local the problem was that German universities had tried to get too much material into three year courses when the new bachelor's came in.
"They stuffed in too much without changing the supervision," said the 29-year-old, who graduated this year from Munich's LMU with the equivalent of a master's degree after going through the old system.