The Hebrew of Isaiah 7:14 doesn't say "a virgin", the Hebrew literally means "the maiden/young woman". Based on the usage of the definite article "the", it implies that the prophet has a specific "maiden" in mind, and I'm of the opinion that she was present at the time. The classical Jewish interpretation of who the woman might be is divided between either Isaiah's wife (which is who I think it probably is) or Ahaz's wife, because of the context. The context excludes Mary, the mother to Yeshua/Jesus because of how long it would be before she was born. Both Isaiah's wife and Ahaz's wife gave birth within the next year, which fits the context and it really could be either one of them. The sign that the prophet gives in verse 14 is not the pregnancy or the birth, it's in verses 15-16. The sign Isaiah gives is that before the boy is old enough to learn right from wrong he's going to be eating luxury foods (cream/butter and honey, both of which require some work and cultivation before eating), and by that time that the war with the northern Jewish Kingdom of Israel and Aram will be over. That's the context if you read the first 13 verses of the chapter, which is why it doesn't work for Mary giving birth to the baby Yeshua/Jesus who lived centuries later.
The first 13 verses of Isaiah 7 introduce the prophecy in verse 14, I'll give you the context, but I encourage you to read the entire chapter so that you can see for yourself that I'm not reading something into the passage that isn't there. There's a war going on at the beginning of Isaiah 7. At this point in history, the Jewish nation was divided into two kingdoms led by two different kings, this is clearly spelled out in the books of Kings and Chronicles. The northern kingdom was called Israel and was led by a king who wasn't descended from King David named Pekah in Isaiah 7, and the southern kingdom was called Judah and was led by a king who was descended from King David named Ahaz. King Pekah of Israel formed an alliance with King Rezin of Aram and the two conspired to go to war with the Kingdom of Judah. Naturally, this frightened King Ahaz of Judah, but Isaiah was dispatched by G-d to calm Ahaz's fears. Isaiah told Ahaz to ask G-d for a sign that the war would go well for Judah, but the wicked king feigned piety and said that he wouldn't dare question G-d. That brings us to verse 14, we're Isaiah says "you're not fooling anyone, I know you're not refusing a sign out of piety. So G-d is giving you a sign whether you want one or not, the young woman will have a son and the war will be over before before he's old enough to distinguish between right and wrong". Isaiah basically said that the war would be over soon and Ahaz's fears were baseless.
It would be nonsense for Isaiah to tell Ahaz that he didn't need to worry because the war would be over in a few hundred years. The war was over just a short while later, which fulfils the prophecy.
There is a minor problem between Isaiah's prophecy and Matthew's mistranslation of it, and the problem is who is calling the child Imanuel, Isaiah says it's his mother ("she will call his name") but Matthew says it's an unidentified group of people ("they will call his name"), and Yeshua/Jesus is never seen being called this anywhere in the NT except where Matthew misquotes Isaiah. This problem is minor because it's obvious that the author of Matthew didn't actually quote Isaiah, and it's this misquote that leads Christians to believe that Yeshua/Jesus was the Messiah based on a prophecy of a virgin birth. This means that the author of Matthew intentionally distorted Scripture to invent a case for the virgin birth and claim it was foretold in Scripture. In reality though, there is no prophecy of a virgin birth anywhere in Scripture, and Isaiah 7:14 is the only passage that Christians use to claim that Yeshua/Jesus was born to a virgin. The reason this is the only passage that's used is because it's the only one that could be mistranslated and isolated from its context to appear to support the virgin birth that Matthew and Luke teach. There are some Christians who say that Matthew didn't intentionally distort the Scriptures because the Septuagint says that the "maiden" in Isaiah 7:14 was a virgin (the Greek is "parthenos"), and the Septuagint was written by the rabbis and should be accepted by Jews as a valid translation. There are three problems with this argument though. The first problem is that it's based on a translation, and a translation is never as valid as the original, it's a principle called the law of best evidence. Also, a translation of the word of G-d is, by definition, the word of man. The second, and the biggest, problem is that the rabbis didn't translate Isaiah in their Septuagint. The Septuagint that the rabbis translated was a translation of only the Torah, the five books of Moses. The Septuagint that the Church has historically used was a poor translation written by Christian scribes, and it's obvious by reading it that they took the misquotes of Scripture that are in the New Testament and inserted it into their Septuagint. This is actually attested to in multiple sources that I don't have with me right now, otherwise I'd tell you the names of the sources, but I encourage you to do some research on the Septuagint and you'll see that the Septuagint of Isaiah wasn't written or authorised by the rabbis. The third problem is that the Greek word parthenos doesn't mean "virgin", it was used the same way that we would use the word "maiden" today. A proof of this actually comes from the Septuagint version of Genesis 34:3, after Dinah, the daughter of Jacob, was raped she was called a parthenos.
I hope this sufficiently answers your question, best of luck,