@Joy69 This is something that I am interested in. My partner has autism and serious mental illness, but for most of our 25 year marriage, he looked and behaved significantly younger than me. In many ways, he was like a teenager in terms of his behaviour.
Then, about two years ago, he began to act much older. He started to shuffle, he started to refer to himself as being 'elderly' and he became very intolerant of change or small groups (he has always found crowds difficult to cope with).
I will not go into too many details, but his mental health/cognition began to decline, and he developed cataracts. His 'autistic' traits also became much more prominent (difficulties with change, not wanting to talk).
A strange incident which may have been something to do with his heart, sent him to A and E and scans revealed serious arteriosclerosis. He remained in hospital for a couple of weeks for tests.
Upon discharge, he barely left the house, and his shuffling became much worse. Early this year, he took an overdose of medication and spent seven months in psychiatric hospital.
Now, he is in a care home, and I still do not know what is really 'wrong' with him, but he still hardly leaves his room, has to be prompted to dress and shower and has lost a significant amount of weight.
I realise there is more at play here than autism, but throughout my husband's decline, the autistic traits have become more and more prominent. I think there may be three things to consider: 1 as we get older, we may have less need to 'mask' or perform, and therefore we can be our 'true' selves, (2), as we get older, sensory issues, the need for routine and other traits which neurotypicals may share with neurodiverse people, become more prominent, or (3) my husband may have an underlying condition (perhaps early onset dementia), in which features of one's personality may become more prominent.
I feel, in my husband's case (he is 64) the third possibility is probably the most likely, and I have read somewhere that people with MH difficulties may be slightly more likely to experience early onset dementia than people who do not experience MH difficulties, and people with autism are statistically 2.6 times more likely to experience early-onset dementia.
This does not in any way imply that having more significantly observable autistic traits as an individual ages is linked to dementia, but in my husband's case, the isolation, need for routine, intolerance of certain sensory stimuli have been exaggerated by whatever other condition he has.