Definitely not. In fact, you would be hard pressed to find a single rishon who was a Young Earth Creationist.
The Ramban says that Bereishis 1:1 describes creation yeish mei'ayin (ex nihilo; something from nothing), and then untold time goes on before the hyle (substance) gets its current forms. But Bereishis 1:2 onwards tells the story after that time.
Rashi (1:1, 2:4) says that none of the chapter is about the order of creation.
The Rambam (Moreh Nevuchim 1:30) says the six "days" are logical steps in Creation and not a chronological sequence. Interestingly, the Haqdamah to the Zohar (4b-5a) says something similar, identifying the days with the 6 ketzavos (directions? sefiros of emotion? all of the above?).
And while the Ramban says the 6 days are literally days, he also says they correspond to the following 6 millennia (and to the 6 emotional sefiros). Rav Eliyahu E. Dessler (“Yemei Bereishis veYemai Olam“, vol II pp 150-154; “Zeman veHishtalshelus”, vol IV, pp 113) shows how the Ramban means that they are actually the same stretch of time. That experiencing time as a line from past to present to future is part of the human condition since eating the Fruit of the Tree of Knowledge and that limitation didn't exist yet. So, we cannot understand how the same stretch of time can be literally one day and also a millennium that seems to be after the day, but that's because of the fruit.
This is consistent with the Maharal who says that while the pesuqim literally describe the history of creation, we cannot picture what existence during creation was like. So, if you think the literal description is of a single creation event that takes 5 days, you're mistaken. No human understanding, literal or figurative, will be correct.
While that may not be what the Ramban really meant, R Dessler didn't think it was kefirah to say that the age of the universe is "only" 6,000 years in one way of looking at time. He explicitly writes that in terms of history, both 6 days and the scientific findings are correct. Just that the 6 days perspective is more usable for our task in life of spiritual growth, and the scientific one is only good for science -- thinking it is primary shows misplaced priorities.
And in either case, the missing time thing would still mean the Ramban is consistent with an old earth.
Similar multiple creation times ideas show up in Bereishis Rabba, which describes Hashem creating worlds before this one and destroying them. Based on which, the Tif’eres Yisrael. He cites an opinion of the tannaim, a central theme amongst the more kabbalistically inclined rishonim, that Hashem created worlds and destroyed them before this one. Dinosaur bones and starlight are legacies of these earlier worlds. The Tif’eres Yisrael did not say anything about evolution, just that this earlier time explains what the fossils are fossils of. In Techeiles Mordechai, R’ Shalom Mordechai Schwadron speaks laudably of the Tif’eres Yisrael’s resolution.
In Gen 1:1, G-d creates ex nihilo (matter from nothing). Then, before verse 2, these other worlds (in this opinion, epochs) rose and fell. Then, there was “chaos and emptiness” from which our world emerged. The universe as a whole, even the planet, can therefor be older than 5758 years.
Since current theory is that the world started as a singularity — IOW, not within the purvey of science, it is all a matter of faith if the ex nihilo was with the intent of the Creator or not.
Rabbi Aryeh Kaplan quotes R’ Yitzchaq meiAkko (a student of the Ramban) who concludes from the Zohar that the first creation was 15.8 billion years ago — the age astronomers and physicists seemed to be converging on in the 1980s and 1990s, given multiple ways of measuring the age. It is unclear that this is truly the intent of R’ Yitzchaq meiAkko, but that’s Rabbi Kaplan’s take. The original lecture to AOJS, which is more complete and persuasive than the mention in his NCSY book, is available for free from the Lulu storefront. This is built on an idea discussed by Rabbeinu Bachya and numerous other kabbalistically inclined rishonim, that of our world being one of a cycle of shemittos, so that there is history and time before our universe.
In contrast, I couldn't find a single source for Young Earth Creationism written before the late 19th century CE.
