was it an electronic monitor or manual?
if you got it three different times its probably correct. even though your systolic is normal your low diastolic would still mean that youre hypotensive but if you really were you'd proabably have some symptoms of that (mainly dizziness). most likely thats just a normal reading for you.
the reason i might be a little worried is that you have an elevated pulse pressure (the difference between your systolic and diastolic). the average pulse pressure for a guy your age is 40 but the average you had between those three readings was 66. its something that could put you at risk for cardiac issues. usually older people have high blood pressure but thats because their arteries are stiffer.