I experienced Zeppelin for the first time in high school when the big local radio station changed to a classic format.
I remember thinking “oh yeah, these guys are gonna be huge.” This was in 1987.
When you hear a great song for the first time, why would you immediately think about whether it was destined to become a classic, even now when classic songs have been a thing for ages?
That’s a weird double step back from getting off on the song itself, right past thinking about what makes the song so amazing, to meta thoughts about its place in history.
And there’s also the reality that ‘classic’ songs were barely a thing in 1971. It was only 7 years since the Beatles broke into the American market. Music was towards the end of a period of extremely rapid changes, but it was still in that period.
I was born in 1970, so can’t claim I remember the first time I heard it.
I had a somewhat sheltered upbringing and wasn’t exposed to much music that wasn’t Top Forty (the seventies to me were Barry Manilow, The Carpenters, Jim Croce, and The Bee Gees). But even so, Stairway was unavoidable. I just didn’t know what it was. Years later, while taking a Driver’s Ed course in high school (so must have been 1986?), I was in the car with several of my classmates when Stairway came on the radio and I exclaimed, “Oh, I love this song!” I still didn’t know the name of it or who sang it. I seem to remember everyone giving me a weird look.
Years later, after I had heard it many, many more times, my brother and I were discussing how some classic rock songs were ruined by overplay on the radio. He commented that he would die of boredom if he ever had to hear Stairway again…and of course, it came on a few minutes later. He gagged, bugged out his eyes, and “died” right there on the couch, and remained dead throughout the song. Let me tell you, Stairway is a long-ass song to have to sit there with some fool pretending to be a corpse! 
I was 17. Instant Classic, yes. I first heard it while riding with some friends, and nobody in that car had any doubt they’d just heard something important.
According to Billboard, Stairway never appeared on the Hot 100 chart in any position. But yes, I’ve never heard one of those “top 500 rock songs of all times” holiday radio promotions where it wasn’t at the top.
Your memories are your memories, but the song wasn’t released as a single, and didn’t chart on the Billboard Hot 100 chart (which is what Kasem’s American Top 40 used for its countdown in the 1970s). I have no doubt that it placed highly on broader “greatest rock songs” lists, which probably weren’t pegged to the Billboard charts.
I was in college then, and I’m sure the campus radio station played it. Moreover, I was a big fan of their first two albums but the third album didn’t work as well for me. The Fourth album, whatever its official name is, had loads of good stuff, hard rock, soft ballads, and this eight-minute masterpiece that started off Apollonian and ended Dionysian in the best 60s rock critic sense.* I told a friend that when listening to it with headphones the top of your head came off as soon as the drums hit. He didn’t think that a good thing, but he was a band geek.
And yes, you do grow tired of the song after a decade or two. But then a decade or two after that you like it again. Age is a funny thing.
*Some rock critic (I’m thinking Robert Christgau although he was talking about a Robert Palmer essay) introduced the concept of Apollonian and Dionysian rock music. Stripped of the jargon, you can think of it reductionistically as soft and loud or smooth and rough. A walk through the great rock songs will show how they combine the two modes into something greater. Not just “Stairway to Heaven” but the two halves of “Layla” or the way Hendrix’s “All Along the Watchtower” layers guitar effects on Dylan’s folk song.
I was similar. It was 1990, sophomore in high school and I was getting out of my 50s and 60s phase. I guess I thought I might as well do rock chronologically. 
Bought Zep IV since all the classic rock kids (and there were tons at my high school) held it up as a gold standard. Loved the album (and all the first five Zep albums); didn’t much care for Stairway. It had been built up to me as this crowning jewel of 70s music, I had somehow missed it my whole life up until then, and I was left with “that’s it?” I’m still likely to skip it or change the station when I listen to IV these days. It just does not resonate on any level with me, except that it has a cool guitar solo.
I don’t think anyone who was into rock in that era ever dreamed that there would eventually be “classic rock” radio stations with highly restricted playlists, re-running songs until virtually everyone was sick to death of them.
And, amazingly, the album didn’t hit number 1 in the U.S., the only album after their first not to do so. If this seems unfathomable, remember that American music had shifted drastically towards soft California rock at the time. The album was released on November 8, 1971 and spent six months on the charts. During that span these albums hit the top.
Santana III Santana
There’s a Riot Goin’ On Sly & the Family Stone
Music Carole King
American Pie Don McLean
Harvest Neil Young
America America
First Take Roberta Flack
Hitting number two was an impressive feat in retrospect.
I was 12. The only LZ song that I liked at that time was Immigrant Song. I came to like more of their music in college but in 1971 they were really nothing to me and I didn’t like Stairway. I still think its average and “too long”. I see it as a rock tune trying to be prog and failing.
Interesting. This certainly isn’t restricted to rock, and the changes mid-song definitely make the music more interesting—maybe not so much for listeners who treat music as nothing more than background noise (but we don’t care about them, do we). Rush is good at this. It could account for why I graduate towards jazz; jazz/rock & similar. It’s a bit like having different chapters, or layers to explore.
21 years old in '71 and didn’t care for Led Zep (except for parts of their first album), feel the same way at age 70. Including Stairway.
I was 11 in ‘71 and wouldn’t get into harder rock for a year or two. But when I did I thought Stairway was boring and too long.
All together there are only about 3 LZ songs I care for.
I was exceptionally unhip (and probably still am), so I don’t recall when I first heard Stairway to Heaven, but I knew it was a classic by 1973.
I knew this because it was enshrined in its full glory on my dorm floor’s Party Tape, which I got to hear a LOT over the next four years.
Even if it didn’t hit #1, Led Zeppelin IV was a steady seller that stayed on the album chart for a long time. It’s also the group’s biggest seller. Even now, it will occasionally pop up on the Billboard Top 200 chart.
Surely by “classic” the OP just means “would be loved by many in the distant future”, it’s nothing to do with “classic rock”. The vast majority of songs written now and in the past are quickly forgotten, Stairway to Heaven wasn’t one of them.
By 1973, it was a joke around the radio station that freshmen DJs would always include “Stairway” in their first show.
In 1970, one of the big Chicago AM stations–I think it was WCFL–had a pre-recorded “Instant classic!” intro it played before a few–veremphasized texty few–songs. Of course, we scoffed at such an oxymoron, yet the rare songs that earned that distinction included “Layla” and “Bridge Over Troubled Water,” and the first time you heard them, you knew you were listening to a superlative song that would become a classic–not just a catchy song, not just a great song, but one that had “classic” all over it. (So not instant, but instantly recognizable as classic.)
Yes, it was a time of extremely rapid changes, but “classic” was definitely a concept back then. Remember that most of us listening to those songs were young, and 7 years is a very long time to somehow who’s 20. I was 13 in 1970, and while I remembered the Beatles’ U.S. advent, it was half a lifetime ago for me and a couple of major transitions for them. It was because of that rapid change that we were able to recognize certain songs as stand-outs that were obviously destined to become classics. Like most of us, I knew I was living in an era of incredible music, and that a few of those songs were very obviously destined to become classics.
As I mentioned earlier, “Stairway” was never released as a 45 rpm single commercially. It did, however, get a promotional release to radio stations in that format. Why, I don’t know, since it was several years old at that point. I seem to recall the record company wanted to release it commercially, despite its age, since it had achieved “classic” status by that time and they probably thought they could squeeze a few more bucks out of it, but that the band had control over it and said no. This may be just legend. Either way, Casey Kasem would not have played it.