I'd recommend checking with your doctor about your concerns at the next visit. Some increase in reaction time is normal but that seems a little young for it to be so noticeable. However, your driving may well be safer for both yourself and others than that of the drivers who are prone to honk at you with impatience.

I'm hoping that the autonomous cars become approved and accepted before too long so we won't have so many drivers who recognize that their skills are decreasing but, unlike you, are unwilling to adopt a car-free lifestyle.