It is available here. http://johnforester.com/Articles/Safety/Cross01.htm
I noticed that the older cyclists seem to be victims of motorists... not some bad behavior on the cyclist's part.
Take a look at this chart showing the ages of the victims in the study and note that the older cyclists tend to be in the categories where the motorist is at fault.
Note the 50th percentile of those cyclists tends to be at or above 20 years of age.
I realize this is ancient data, and it was taken from police reports which themselves may be biased. The data also is from a very narrow set of dates and a very specific location (Santa Barbara in the early '70s)
But none the less, it tends to show that motorists are the leading cause of bike/vehicle collisions for older riders. At least in this '70s era report.