Is it possible to be diagnosed with sickle cell anemia at 43? even without ever experiencing any symptoms of the disease?

Unlikely: You may be a sickle carrier. Even the milder sickle variants -- sickle-thal, sickle-c -- usually get noticed beforehand.

Possible, but...: Most people will have symptoms of enough severity to be diagnosed before adulthood. That being said, there is variation in the severity of sickle cell disease, most likely due to a number of other genes that modulate the symptoms. Thus, it probable is quite rare, but there could be that individual with a particular genetic makeup that has minimal disease that goes undiagnosed.