PREhypertension is from 120/80 to 140/90 so that one is right on the border but please don't let one reading freak you out!!! When my first wife just up and left me, I was having some REALLY high readings like 160/100 and was put on medication, minimal dose.
Things settled down, I moved on and changed doctors. The new doctor saw that I was on the med so he just kept me on it (don't get me started about doctors and med's). I was on this shit for 11 years because of a short term, situationally induced rise in BP. Did I need it all that time? Probably not!
Later on, because the MD also wanted to put me on cholesterol lowering meds, I finally said "WAIT, can't I do something to prevent this???" Well, hell yeah, often you can! I avoided the new meds and GOT OFF THE BP meds by starting to learn about diet and exercise (which you have done) and buying a home monitoring device to take readings throughout the day instead of relying on that one reading in the doctor's office.
Who knows, maybe the nurse that took your reading bent over right about then and caused yours to go up (the BP, that is!) In my case, my readings will ALWAYS be high the first time (white coat syndrome) but, if they take it at the end of my checkup, it'll be pretty good. I get really low numbers after first getting up at home.
So, the point is to not judge your overall health on one reading. That doesn't reflect the state of your BP health, only what it was at one point in time! You need more than one reading to make any kind of determination. I lift heavy all the time and used to be considered hypertensive and on meds but no more. By the way, I'm just shy of 52 now.
From what I've read, there is some benefit to your BP to do some aerobic exercise but I certainly wouldn't get too carried away. Personally, I'm more interested in overall fitness so I use an overall fitness training approach which does has some limited aerobic stuff.