GSM It is 12 years for the PhD. He went to the States when he was 21, presumably post BSc and is now 33. he went, initially for a year, which is odd because a PhD requires 3 year's study. He claims he didn't finish it because he had to do tutoring to cover his keep. Another figleaf I think, because many students at all levels, here and in the US, especially the US, juggle work and study. DS did, as did most of his friends, one or two ran over a year, but universities put stop notices on how long you can spin out studying for a PhD, after which you are signed off and are no longer on the university roll.
I suspect, and this is no disrespect to the OP, but her son has been, telling her a tissue of lies, knowing that she doesn't know enough about the arcane workings of academic life or AI to really probe what he tells her.
Sadly, I think this is a case of a young man with autism ADHD, who cannot cope with normal life and has retreated back home to avoid a life outside he cannot cope with.