I asked this question yesterday, perhaps a bit too hastily:
I think I bit off more than I can chew with this question, as I know little about the maths surrounding the prime number theorem. However, I asked the question assuming that any proof that
$$ \displaystyle\lim_{n\to\infty}\ \frac{p_n}{p_{n+1}} = 1\quad \text{where}\ p_n\ \text{is the n-th prime number}?$$
will require knowledge of the PNT, especially the proof of the PNT itself, which I do not have. Is there an elementary proof of the above statement, that does not require knowledge of the PNT or related facts, or difficult number theory?
For example, the proof that there are infinitely many primes is not too difficult to understand, and doesn't require any advanced number theory. So I am wondering if there is a proof that the primes are eventually relatively close with a similar level of difficulty to the proof that there are infinitely many primes. Sorry for not providing this information sooner.
The first elementary proof of the PNT famously happened when Erdos proved that $\lim_{n\to\infty}\frac{p_n}{p_{n+1}}=1$, and then Selberg combined that with some of his other works to derive the PNT in an elementary fashion. If you wish to call Erdos's proof of the $\lim_{n\to\infty}\frac{p_{n}}{p_{n+1}}=1$ an "Elementary proof without prime number theorem related maths" then you have your answer, but seeing as this was the crucial step missing for a full elementary PNT proof I'd call that a stretch. I don't think that there is any more complete answer to your question one can give, short of transcribing a rendition of Erdos's proof.
An account of the first elementary proof of the PNT is here. Be warned, however. What Erdos and Selberg call elementary might not look so elementary to you.