Autism is often painted as a childhood condition, usually spotted in the school playground when social quirks or communication differences raise eyebrows. But what happens when those children grow up without anyone connecting the dots? According to new research from King’s College London, the answer is unsettling: most autistic adults over 40 are still flying under the diagnostic radar.The review, published in the Annual Review of Developmental Psychology, estimates that a staggering 89 per cent of people over 40 with autism remain undiagnosed. To put that into perspective, while around 23 per cent of autistic children under 19 are missed, nearly 96 per cent of those over 60 have never been recognised as autistic. That’s not just a gap; that’s a canyon.The Age FactorWhen the researchers broke it down by age and gender, the numbers looked even more lopsided. Among men aged 40 to 59, more than 91 per cent had never been diagnosed. For women in the same age group, the figure was almost 80 per cent. By the time people reached their sixties, both men and women crossed into the 96 to 97 per cent range of being undiagnosed.Compare that with the 20 to 39 age group, where roughly half remained undiagnosed, and the generational divide becomes clear. Today’s younger adults are far more likely to be spotted, assessed and supported. Older adults, meanwhile, have often been left to muddle through without a name for their lifelong differences.Why It MattersGavin Stewart, lead author of the study, explains that a lack of diagnosis means many autistic adults were never offered the right support, leaving them more vulnerable to age-related problems. These range from social isolation to poor physical and mental health.The review found that autistic people in middle age and beyond have higher rates of almost every health condition compared to non-autistic peers, like heart disease, neurological issues, autoimmune disorders, gastrointestinal problems, anxiety and depression. Add age-related conditions like osteoporosis, arthritis and Parkinson’s disease, and the picture gets even more complicated.Even more concerning, autistic older adults were six times more likely to report suicidal thoughts or self-harm and four times more likely to develop early-onset dementia.The Hidden StrugglesThe study highlighted another layer of challenge: healthcare itself. Many older autistic adults face obstacles in accessing medical support due to communication differences, sensory sensitivities or simply not knowing how to navigate the system. Combine that with a shortage of healthcare professionals trained in recognising autism in adults, and it’s no wonder so many cases slip through the cracks.Professor Francesca Happé, co-author of the review, stresses that this is a global public health issue. “Understanding the needs of autistic people as they age is a pressing global public health concern. As autistic people age, the nature of the challenges they face changes. We must adopt a lifespan approach that funds long-term research, integrates tailored healthcare, and expands social supports so that ageing autistic people can live happy and healthy lives,” she says. In other words, autism doesn’t disappear after childhood, so neither should support.Lost in the ShuffleThe findings also suggest that research into autism may have been skewed for years. If most older adults remain undiagnosed, then studies have largely overlooked them. That means our current understanding of how autistic people age is incomplete at best. No wonder policies and services have not caught up.Employment struggles, strained relationships and social isolation were all noted as common experiences for older autistic adults. Without the framework of a diagnosis, many never knew why they felt out of step with the world, and their difficulties were often chalked up to personality flaws or “just how they are”.Why a Diagnosis Still MattersIf you’re wondering whether getting a diagnosis later in life makes a difference, the answer is yes. Recognition can bring clarity, opening doors to support systems, healthcare adaptations and even financial benefits. It can also reshape how family, friends and colleagues understand a person’s behaviour and needs.The NHS encourages adults who suspect they might be autistic to speak to their GP and ask about a referral for an assessment. Specialists can help by gathering life history, speaking with people who know you well and observing how you interact with others.A Call for ChangeThe review ends with a clear message: it’s time to stop treating autism as a childhood-only issue. For too long, older autistic adults have been invisible, their experiences untold and their needs unmet. With diagnosis rates still alarmingly low, researchers are urging more studies, better services and a cultural shift that embraces autism across the lifespan.