I guess it should come as no surprise that your motor skills decline with age. Your reaction times decrease, and you generally can't do things as fast - or as well - as you could when you were younger. If that weren't the case, you would see a lot more 50 year old baseball players. So should it be a big surprise that your ability to perform well on field sobriety tests (FST) also decreases with age?
When the FST's were implemented NHTSA recognized that there might be problems with older persons - which they characterized as over 65, A recent study in the United Kingdom shows that the problems actually starts when someone hits 40. The study was designed to compare the Field Impairement tests that were being used with a Roadside Impairment testing device that utilizes a handheld computer. The FIT's include the same tests used in the United States, such as the walk and turn, one leg stand, Romberg test and finger to nose (although the last the two aren't used as much anymore). They utilized subjects who were given measured doses of alcohol and those given placebos. The percentage of persons who took the placebo and failed the tests drastically increased once the subject hit 40. For individuals 41-50 the failure rate was actually higher for the individuals who took the placebo. For the other age ranges the failure rate to close to the same.
So what should this tell us? One conclusion is that the FST's are nothing more than agility drills, which have nothing to do with driving. That would certainly explain the failure rate of the older group. The other - less sweeping conclusion - is that the FSTs are not accurate for individuals over 40.
If you are over 40 and the State is relying on field sobriety tests you- and your lawyer - certainly need to be aware of this study. And use it to your advantage.