A few comments a bit scattery but maybe you can pick something useful out of them.
I've taught many children diagnosed with ASD - including two months in a specialist ASD school. It's a heck of a wide spectrum - down to the ones who do not understand langauge and will give you a sentence all as one word because they know it's a sound to make when you want something; and others who are mute, or can only screech.
It's said that ASD is underdiagnosed in girls because at first they get by on copying their pals; later (teen-ish) when female competition takes off they realise they haven't a hope and the anxiety and depression really take off. And temper/panic blowups, or self-harming.
We have a 50ish friend who I suspect is ASD but she doesn't know and I'm not sure that it would necessarily help to tell her, because she might add it to the list of 'things that are wrong with me' - for some young people I've taught, it's a badge saying'don't expect anything from me' - a kind of get-out-of-work chitty cum self-stigmatisation. [Some of the low-ncome parents can be keen to secure a diagnosis for their children, it results in extra financial allowances that help them with their budgetary struggles.] In any case our friend has finally found someone who loves her which is what she needed most; but she has gone from one job to another, each time eventually coming to the conclusion that the workplace people 'have it in for her.'
At a higher level of the spectrum, apart from things like OCD and food faddishness the major problem is in social understanding and communication - and we all know what a subtle game that is. But it can be taught or learned, it's just that the learning will be a slow process and the person will seem socially reticent or awkward; maybe more can be done to teach them conversational strategies so they can make relationships more easily. Doesn't always stop you making a living - think of the BBC's Chris Packham; can be an advantage in maths, sciences, engineering etc where memory, attention to details and ability to focus for long periods are advantages (incidentally, in the Army some members of the SAS might be somewhere on the spectrum? I remember reading Andy McNab saying one of his lot couldn't wait to get home to clean his windows!); but it is a more difficult path for many. Part of the problem is other people's atttitudes of course.
Looking at other comments here, yes, I think there's a lot of undiagnosed adult cases, ASD diagnosis has extended greatly in latter years so older people will probably have been missed. Worth trying for a diagnosis because if an employer takes you on on that basis they will have to make reasonable adjustments and to be fair many do.
Also, there are other conditions that may have ASD-like features, e.g. dyspraxia (which can also manifest as physical awkwardness) and foetal alcohol syndrome (whch can link to a host of symptoms.)
A challenge for the ASD person is dealing with a vague sense of disconnection, aloneness, of being on the wrong foot somehow; anxiety and depression are common and kindness and understanding from others can go a long way to help. But not just condescension - as I said, one can learn and develop skills and confidence.