Even though the adolescents may have reached a length of around 10ft, they struggle to deal with larger prey because their jaw bones are too soft.
Scientists in Australia found that because the fish grow so quickly the cartilage takes a long time to harden.
That means until they reach maturity at around 15 years old they have to make do with a diet of small fish rather than their traditional larger prey.
It could also explain why many attacks on humans are aborted – as the jaws of the sharks are too vulnerable to damage.
The sharks may even be vulnerable to predators themselves – especially killer whales.
Toni Ferrara, the lead author at the University of New South Wales, Australia, said: "It is hard to believe, but at this size great whites are basically just awkward teenagers that can't hunt large prey very effectively.
"It seems paradoxical that the iconic jaws of great white sharks – made infamous by the classic Steven Spielberg movie Jaws – are actually rather vulnerable when these sharks are young.
"Great white sharks are not born super-predators, they take years to become formidable hunters."
The study came up with their findings after catching a 10ft great white shark as part of the New South Wales Bather Protection Programme in Australia.
Scientists used sophisticated three-dimensional computer models and advanced engineering techniques to examine how different sharks hunt and kill prey.
Detailed computer simulations examined the feeding behaviour of two threatened shark species: the harmless grey nurse – or sand tiger – and the notorious great white.
Digital models revealed that the jaws of grey nurse sharks are spring-loaded for a rapid strike on small, fast-moving fish, while those of great whites are better suited for a powerful bite on prey ranging in size from small fish to large marine mammals.
The study co-author Dr Stephen Wroe, at the UNSW School of Biological, Earth and Environmental Sciences, said: "We were surprised that although the teeth and jaws of our sub-adult great white shark looked the part and the muscles were there to drive them, the jaws themselves just couldn't handle the stress associated with big bites on big prey.
"The reason for this appears to be that until great whites reach a length of about three metres or more their jaws haven't developed enough stiff mineralised cartilage to resist the forces involved."
Dr Vic Peddemors, of the NSW Cronulla Fisheries Research Centre of Excellence, added: "This study may also explain why many of the shark attacks off NSW are aborted after a single exploratory bite, as the great whites involved are usually juveniles that might sustain jaw injury if they persevered with the attack."
The study was published in the Journal of Biomechanics.