All his life Andrew Davies has had a sense of not fitting in, that he was somehow broken, weird or there was something wrong with him.

That was until he discovered he was autistic at the age of 70.

“It’s just who I am and how my brain is wired… how I experience the world is just different,” he said.

Research has suggested that like Andrew, there are many others who have spent a lifetime not knowing they are on the autistic spectrum.

Between 250,000 and 600,000 people over the age of 50 in England may be autistic but undiagnosed, a study of primary care records in England has suggested.

That would mean more than 90% of autistic people over 50 were undiagnosed, its researchers have said.

“Autism was seen for many years as a childhood condition but it’s a lifelong condition and as people get older they remain autistic,” said Andrew.

Andrew, now 72, retired in 2019 following a long and impressive career.

He was a minister for the first 10 years of the Welsh government and the assembly member (now known as Member of the Senedd, or MS,) for Swansea West from 1999 to 2011.

After standing down from the assembly he was chairman of what was then Abertawe Bro Morgannwg University Health Board for six years.

Perhaps not the most obvious line of work for someone who says they have “often struggled understanding and dealing with other people”.

“I can be in a group and it’s keeping up with conversations, knowing what to say… it’s not knowing the rules of small talk,” said Andrew, who lives in Mount Pleasant, Swansea.

From childhood he preferred being alone and one-on-one friendships to groups.

This became harder to deal with in secondary school.

“I just completely struggled really,” he said.

“I felt there was something broken, there was something weird, something wrong.”

He found the social rules and structure of working life easier to navigate but would often feel “bombarded” and “peopled out” by the end of a long day.

“I suspect people may have thought ‘oh he’s pretty standoffish’ but it’s a combination of shyness and not knowing what to say,” he said.

Andrew also experiences hypersensitivity.

“Discos and rock concerts I never really enjoyed, I found the sound for example and the lights almost overwhelming and uncomfortable,” he said.

Other sounds, be it his wife popping chewing gum or a neighbour’s dog barking, and some smells, such as congealed fat or grease, and sights such as fluorescent lights, have always made him very uncomfortable.

“I just have to get away,” he said.

“You try to ignore it but it’s a physical, visceral reaction.”

Something that has always served him well in work he now knows to be another trait of autism – intense interests, also known as hyperfixations..

He said he often became preoccupied with a topic he was interested in, throwing himself into intense research.

“I want to really get to know that issue in depth whereas most people will think ‘that’s interesting’ and move on,” he said.

He said researching autism had become “yet another rabbit hole I’ve disappeared down”.

It was this tendency to become overly engaged in topics that he first identified as a possible autistic trait in himself.

He was chatting to a colleague who had recently been diagnosed with autism.

The colleague said he had been working with a consultant psychiatrist who took him to one side and said: “I hope you don’t mind me saying this but you’ve got all the classic signs of autism.”

Seeing a parallel between the colleague’s detailed research and long emails and his own “the penny dropped”.

Andrew started reading and listening to podcasts about autism and decided to take the online questionnaire designed by psychologist Prof Simon Baron-Cohen.

“I came out very firmly in the middle of the spectrum,” he said.

He then decided to seek a formal diagnosis, discovered the NHS waiting was three to four years so in the end went private.

What does having a diagnosis mean to him?

“It was just having that confirmation really… I wasn’t broken or weird, or something wrong, it’s just who I am and how my brain is wired,” he said.

“When you get to this age you look back on your life, from role to soul.

“I think it helps you come to terms with things that have happened in your life.”

Andrew has experienced depression since he was a teenager – research suggests autistic people may be more likely to experience depression than non-autistic people, according to National Autistic Society.

He has also experienced periods of ill health which he now believes to be autistic burnout.

Figures suggest people over 50 are not being diagnosed with autism at anywhere near the rate of children – one in 34 children have an autism diagnosis compared with only 1 in 6,000 adults over 50.

“There’s likely to be a very large underserved population who deserve to have the support they need,” said Dr Gavin Stewart, a research fellow at King’s College London, who is interested in ageing and autism spectrum disorders.

He said one reason for older people going undiagnosed was in the ’60s, when they were in their youth, autism was viewed as a very rare condition “whereas today it is viewed in a far more common way and the prevalence rates reflect that”.

He said for many older people receiving a diagnosis was a “lightbulb moment” and meant they could better understand their life experiences and it also opened doors for help and support, for instance from employers or those providing residential care.

He would like clinicians working in older adult services to be more able to recognise undiagnosed autistic people.

“We know that autistic people often need additional help and support throughout their lives to support them with their mental health and ensure they’re living happy lives,” he said.

“Having the right help and support could be a real key factor in ensuring that they’re ageing well and I think that everyone is entitles to have the best life that they can.”

Information and support about autism is available via BBC Action Line.