Again in UK, found this centre Rice locally which is doing clinical trials here are some of the stuff they have done in the past. It also says about being over 55 for most of the trials I think. http://www.rice.org.uk/previous+clinical+research
It also says if you "have a diagnosis of dementia or Mild Cognitive Impairment you may be eligible to take part in one of our clinical trials exploring new drug therapies for treating dementia and memory decline." http://www.rice.org.uk/research+volunteers
but as we know, it is often better to help things in advance of this stage.