free for 8 months, now my Dr. doubles my tegretol dose

I'm a senior that has been on 400 mg of tegretol XR for several years and totally free of any seizures for 8 months.
 
1.  Does that sounds appropriate ? 
2.  Do seizures increase with age ?  (I'm 73)
3.  What is the minimal does of tegretol XR to be effective ?
 
Thanks all,
Gene, Floridia