There are multiple problem at the age 94 years but he needs to take medication regularly as far as metformin use in renal failure
has limitations at levels >1.7mg%(>15 micromols/dl). So check renal function as sometimes it may cause lactic acidosis
,avoid hypoglycemia that is low blood sugar
if kidney problem is more other medicine to keep sugar level may be used.You may see a Nephrologist
and Cardiologist for opinion.