I can relate somewhat from the other end, as I am close to his age.
I think the most pressing need is to identify the issues are that are holding him back from becoming more independent, which are likely many of the same that are irritating her. I think it's also important to consider that the very fact, he is still at home and she hasn't kicked him out, is indicative of a certain relationship between them, which may well have had a pervasive influence on his development. Not exclusively a negative influence, but I was also parented very intensively, and I'm beginning to wonder how much this strong and supportive parental influence masked underlying issues and deficits that would have otherwise been handled long ago.
I did live on my own for quite a while, when I was attending graduate school, and took care of my own finances, cooking, cleaning, etc. However, I was not successful in my program due to social issues, and so now I have had to move back in with my parents. Us aspies are often precocious and ahead of the game growing up, but then when we realize that the career world does not live up to our high expectations, and we can't easily live up to its expectations, we feel that something is deeply wrong.
This disillusionment is common among even people off the spectrum, though due to their greater flexibility, they seem to adjust faster. However, it seems that people without AS go through the worst of this upheaval earlier, when their peers also are, whereas for a "mid-20s teen" it's harder to catch up because most of one's education/career peers are ahead socially.
Also, in my case, I have a physical health issue that started around puberty and greatly decreased my frustration tolerance while increasing my obsessiveness even beyond what it would be from "just" Asperger's. To alleviate this required extensive treatment with antibiotics, various supplements, etc. over many years. I have heard that puberty is rough for many on the autism spectrum, sometimes even going as far as causing seizures or reactivating other serious disorders that were formerly under control. If a person is smart and studious and lives in a familiar environment, emotional issues like depression, irritability, etc. can be ignored (by the person himself/herself), until then when he tries to live on his own, they "catch up".
So if that woman does have her son move out, he should definitely have a therapist of some kind he can talk to, plus the mother should think about whether some of his behavior may be letting out some tension that must be eased before he can succeed in the world. Otherwise, when he leaves his familiar environment, he will likely get into arguments with his employers--due to inflexibility or overstepping boundaries--and burn bridges with friends, etc. I could imagine that some on the spectrum may actually be prone to getting into violent fights if they go out in the world before they have gained a measure of control over their internal and external environment.
I would also encourage him to keep home/career life balance. I realized a while back that I was expecting my career life to be kind of both a career and a hobby at the same time, which wasn't healthy. Encourage him to pursue things like exercise, art, etc. that can act as outlets, so he doesn't need his work to be an outlet (or can even be an "inlet", in the sense that it makes him have to give up/compromise).
That's all I can say...