Anything over 60 is fine, people stress way too much over cadence when it's really not that important until you're years into your cycling hobby. As a mountain biker, my cadence will go anywhere from 40-ish to well over 100 on any given ride, it's not a big deal. Yes there's an ideal cadence for max efficiency at higher power outputs which is around 85-90rpm, that's what you'd ride at if you're training hard or trying to win a race but for recreational riding and especially as a novice, it just doesn't matter yet.
Ride whatever cadence feels best until you get serious enough about cycling that you're shaving your arms & legs for drag reduction & extra speed. 70rpm is perfectly fine and it's not going to wreck your joints or cause any bio-mechanical issues.