Learning at your own pace is a key feature of the reforms set out by Mike Tomlinson's working party.
Report envisages many more mixed-age classes
"Programmes and diplomas will not in general be linked to specific age ranges within the 14 - 19 phase," says its report on secondary education in England.
"Young people should be able to progress through the system as fast as they are able."
And, indeed, leave education and return later with credit for what they had done before.
At the launch of the interim report, Mike Tomlinson said he did not think this was as radical as some people made out.
A number of schools already had students younger than 16 doing GCSEs, for instance.
"Every teacher in the land knows young people do not progress at the same rate," he said.
"Teaching by age could in time be replaced by teaching for stage, allowing students to progress at their own rate."
'Challenging' for teachers
A member of the working party, Marlborough College headmaster, Ed Gould, said mixed-age groups were perfectly possible.
He had known someone of 18 - who had fallen behind through having cancer - working alongside students as young as 14.
Ed Gould says some schools do this already
"At the moment they have the same age but a wide range of abilities," Mr Tomlinson added.
"Which from my experience as a teacher is on of the most challenging aspects of the job."
Another member of the team, the vice-chancellor of the University of East Anglia, David Eastwood, said people should not necessarily assume that the new advanced diploma would be the same as A-levels.
"So what we may find is that learners will want to stay in the framework for rather longer."
But "appropriately qualified" students might well be taken on at a younger age by universities - which already happened to an extent.