It is true that blood pressure normally should be within the 120-140 (systolic)/80-85 (diastolic) range. Low blood pressure like yours is considered a disease only if causes you problems (dizziness, blurred vision etc.). The greatest problem that hypotension can cause is losing consciousness (syncope) and possible trauma when falling down. You didn’t mention any of these symptoms. If your body has adapted to such low blood pressure and there aren’t any symptoms it seems that you needn’t be worried about the low blood pressure.