If someone convinced you that an old Earth would somehow disprove anything in the Bible, they made some error.
In scripture we only know the rough timeline by genealogy from
after Adam and Eve left the Garden until Christ.
That's not the same as knowing how long the Garden lasted (with the Tree of Life, and God Himself for Whom time is nothing in the Garden....).
Nor is there anything in scripture that says how long passed during the Gen 1:1 creation of the Universe and of Earth,
before the moment in Gen 1:2. Those are unknown amounts of time.
If someone claimed it's biblical that either of those times were short, they were wrong to claim that's a biblical idea. It's their guess.
The scripture doesn't say how long those times were because we do not need to know for the purpose of faith. Faith
isn't to merely see or have proof, but instead faith is believing in what we
cannot yet see.
If the Bible had told us the exact age of the Earth or the Universe (or the difference between the two, etc.) -- example: "...and the Heavens were 9 thousands of thousands of thousands of years old when the Earth was born..." (what the Bible intentionally
does not tell us) -- and then science confirmed it, faith would be preempted, precluded.
That information in scripture would preempt and thus prevent faith.
You do not have faith that you have a car, but mere knowledge that you do. Knowledge isn't the same as faith.
Hebrews 11:1 Now faith is the assurance of what we hope for and the certainty of what we do not see.
Easy proof would prevent faith from being available to happen. We'd merely have confirmed God, without having to have any faith.
But God wants us to trust
without easy proof.