ADHD in older people

What is the prognosis for untreated ADHD for older men? My husband is in his mid-fifties, was diagnosed with rather severe ADHD about 15 years ago, and has refused treatment. At first he did try to understand some things about his ADHD and made efforts to learn to be more focused, which he thinks is about all he needed to do. We are approaching our older years and he seems to be getting worse in many ways: more forgetful, irritable, angry/short-tempered, unwilling to listen or participate in the marriage, I could go on. He only will do anything if he “feels like it” which of course nobody ever feels like taking out the garbage or feeding the dogs. I am reluctant to have the grandchildren around him because he might yell at them for no reason, just because he is frustrated with something. I think he is getting worse, but it may be just that my patience is wearing thinner. Here is my question: as an untreated individual approaches older years, are they likely to become worse, better or stay about the same? I realize that every case is different and I am asking for a rather specific answer for a generalized question. Thanks for your help and for this website.