What are dangers for using carbidopa at the age of 50?

Not dangerous per se: I presume you mean using sinemet, (carbidopa and levodopa) which is a combination of Carbidopa and levodopa, for parkinson disease. There are no inherent dangers with using this medicine. If, however, the patient is on high doses, the patient will likely develop dyskinesias which are "excess" movements of the patient. Most patients prefer dyskinesias to being frozen, but sometimes the movements can be extreme.