Lead author Prof Susan Sawyer, said delays in young people leaving education, settling down and becoming parents, showed adolescence was now longer and argued that policies that support youth should be extended beyond teenage years.
Countries such as New Zealand already treat children who have been in care as vulnerable until they are 25, allowing them the same rights as youngsters
"Age definitions are always arbitrary," she said, but "our current definition of adolescence is overly restricted."
"The ages of 10-24 years are a better fit with the development of adolescents nowadays."
However other academics argued that just because young people were unmarried or still in education did not mean they were not fully functioning adults.
But Dr Jan Macvarish, a parenting sociologist at the University of Kent, told the BBC: "There is nothing inevitably infantilising about spending your early 20s in higher education or experimenting in the world of work.
"Society should maintain the highest possible expectations of the next generation."
Prof Sawyer also admits there could be downsides to he plan, particularly if youngsters were no longer seen as responsible or capable of full engagement in society until they were 24.
"Such a view would risk disenfranchising adolescents and undermines their rights to fully participate in society," she added.
