Hi sals and welcome to this forum .....
If you have a 4.5 cm acoustic neuroma, it is indeed in the large category. I am not a medical professional (nor are the users of this forum), but it does seem a bit unusual to wait and watch that large of an AN.
As for surgical removal at age 75, much depends upon your overall general health and potential anesthesia risks. I am not sure why the neurosurgeon feels the balance and tinnitus would be worse after surgery. Granted, it may not be any better than it is now, but that is very difficult to predict.
If your tumor is not pressing on the brainstem currently, you could feasibly live out your natural life if it does not grow any further.
You do not say where you are located, nor which doctors you have consulted. If I were you, I would send my MRI to a well-known doctor, who successfully treats acoustic neuroma patients frequently, for another opinion.
Many thoughts and prayers.
Clarice