i think the age 70 thing comes from enterprise bc if i remember correctly, t'pol went into an "early" pon farr in her 60s. but i don't remember if that was even implied to be her first or if it was just earlier than it should have been based on when her last one was. regardless, enterprise is full of contradictions to previously established canon, and they didn't even want to be called star trek at first and only accepted the name when they realized nobody knew what the fuck "enterprise" was and no one was watching it, so i'm fine ignoring most of that series.
the first time pon farr is mentioned in canon is in the season 2 premier of tos, "amok time." in tos, spock is in his late 30s, and for him to have believed he would be spared the suffering and embarrassment of pon farr until it suddenly hit him just then, that implies two things: 1. this is his first pon farr, and 2. it's later than he would have expected it to normally happen.
but then, in the search for spock, after he has died and been reborn and is experiencing accelerated maturation, he appears to be in his late teens or perhaps his early 20s when he inexplicably experiences what would then be his "first" pon farr.
similarly, in voyager's "blood fever," vorik goes into pon farr in what must be his early 20s since he's implied to be fresh out of the academy. the facts that he isn't married and he didn't think to prepare for or anticipate this before it happened would imply this was also his first time experiencing pon farr.
interestingly, tuvok, who is 107 at the start of voyager, married his wife t'pel relatively late, at age 40, seeming to imply that, like spock, he also experienced a late pon farr for some reason, or he experienced ~3 pon farrs while unmarried.
which to me adds further evidence toward my theory that sexually active vulcans don't experience pon farr, OR they do but it's not as intense so don't really notice it beyond being like "wow i was really horny last week for some reason. huh. anyway."
tuvok is shown to have loved at least one other woman prior to his wife (though they were teenagers and there's no evidence he ever slept with her), and it's shown time and time again that he had a somewhat unorthodox and even rebellious youth by vulcan standards. plus, his family really respected and strived to emulate spock and sarek's family, so it might not be unreasonable for tuvok's father to have turned a blind eye on any initial reluctance to marry on tuvok's part.
and then with spock, until strange new worlds came around and showed spock regularly engaging in premarital sex, the fact that he didn't experience pon farr in his original body until he was in his late 30s but experienced it at around the typical age after being reborn seemed somewhat contradictory. perhaps, then, spock did experience a cycle or two of pon farr as a younger man but just didn't notice it. or he didn't experience it at all because it's some kind of biological failsafe that only kicks in when the situation is dire and the body realizes this person isn't going to have sex, and therefore likely won't reproduce, unless they absolutely have to.
not to mention the whole romulan thing. romulans only left the vulcan home world a thousand years before their reemergence. that's not enough time to evolve to be biologically different. but there's no mention of a romulan pon farr. so either they don't experience it because they don't force themselves to abstain from sexual activity as part of their emotional repression techniques, or they do but they don't notice it because they're not trying to deny themselves anything their bodies are asking for. (or maybe they teach it differently than vulcans do. instead of it being some shameful, uncontrollable urge that they have to keep in check and have designed parts of their society around to accommodate it, they're just like "okay so our fertility cycles are roughly 7 years in length. you may notice an increase in libido at the peak of the cycle, but that's to be expected. it's just your body's way of telling you it's ready to make a baby. if you don't want to do that, use protection. if you have any questions, let me know, or there are also these pamphlets and these websites where you can learn more. now back to your regularly scheduled battle tactics lessons.")