Childhood has meant many different things over the centuries. The transitional years of adolescence, in particular, have come a long way since they just meant smaller, cheaper, more biddable adults capable of factory work and helping out on family farms. It is only in the last 80 years or so that the teenager has come into existence, as a demographic with whole industries devoted to serving its interests – and mopping up its pocket money.

One of those industries was publishing, which responded in the 1960s by developing a market that had been identified by librarians more than two decades earlier: young adult (YA) literature. This highly profitable sub-sector, aimed at filling the gap between childish and grown-up reading, has been around long enough now to offer valuable insights into shifts in social attitudes.

So research released last week, which suggested that 74% of YA readers were over 18 years old – and that 28% were over 28 – is worthy of attention. The report puts the continuing appeal of YA down to reading for comfort, as a defence against the stresses and strains of “emerging adulthood”, among a generation that is taking longer to reach “adult” life.

Nearly a third of the readers were aged between 18 and 22, thus falling well within the new parameters of adolescence suggested by advances in brain science. Another third were aged 23 to 34, so benefited from the boom years of child and YA fiction, when the unparalleled success of JK Rowling’s Harry Potter series inevitably distorted the picture. The sector as a whole has since shrunk.

What qualifies as YA has always been approximate and market driven, to the extent that some books – such as Mark Haddon’s The Curious Incident of the Dog in the Night-Time – have been simultaneously published in both adult and teenage editions. Film, stage and TV adaptations, meanwhile, have drawn older readers to the work of crossover writers such as Neil Gaiman, Malorie Blackman or – more recently – the graphic novelist Alice Oseman.

But these caveats don’t mean that YA literature has nothing to tell us about the world – as was made clear by two top 100 lists published six years apart by Time Magazine. Editors of the lists admitted that when they published the first ranking, in 2015, they had no idea “how drastically the category – what it represents, who it serves and whose voices it centres – was about to shift”. So in 2021, they booted out half of the previous entries to reflect the impact of the #ownvoices movement, hugely increasing the representation of previously marginalised groups. Out went Charlotte’s Web and The Hobbit. In came a slew of more recent novels.

It remains to be seen which of the two lists will seem more relevant in a decade’s time. Their coexistence makes the point that older readers may not only be reading YA novels for different reasons to younger ones, such as solace rather than exploring their identity, but also may be embracing a significantly different body of literature. Nostalgia can buttress older titles against the caprices of the market.

What is undeniably true is that books discovered in adolescence often stay with readers, becoming part of their emotional and intellectual scaffolding. The important thing at any age is not so much what you read, however, as having access to all the benefits of being a reader.