I think it is becoming increasingly common for adults over forty to be diagnosed with ADD/ADHD simply because there is much more known about it know then there was back in the day. Also, it was not until the 90's that ADD/ADHD started to be regarded as an actual condition. Before, it was seen as the equivalent of metal retardation or mental illness so those who had been diagnosed were seen as stupid. As mentioned before, there is so much more knowledge these days that kids are able to be diagnosed at very young ages.