average is 120/80mmhg. but it rises by 5-10 mm hg after 60 yrs of age every decade. so at 70 yrs 130/90 can be normal. and 80-yrs 140/100 can be normal and so on. this is due to the fact that in old age arteries become a bit hard and less elastic,so to supply equal amount of blood more pressure is needed. in old age it depends also on any sort of symptoms of high BP such as headaches,dizziness, etc.and other diseases associated with high BP such as diabetes, kidney problem. but still the best thing to do in hypertension is to take treatment after bp goes more than 140/90 as complications are largely preventable by early treatment.