Recalling the phrase: "In the beginning was the Word, and the Word was with God, and the Word was God ..." we can observe that Catholics believe that there was a beginning ... from nothing ... thanks to God.
Conversely, one might mull on the fact that there cannot be a beginning if the concept of eternity works both ways.
Those things that we call the universe, time and space each only exist as a temporary ‘island’ within eternity.
There was a beginning of time and space - and of the temporary parts of creation, just like an island has a north shore.
In the same way: there will also be an end of time and space and the other pieces of temporal creation, just like an island has a south shore.
While we move and act for a few short years on the island, eternity is waiting for us. That reality - outside of time and space - is our true home.
One day the island isn’t going to be around anymore. But we will be.
Well, hope this flawed analogy was helpful.
From my perspective, eternity cannot work both ways. God created time, existing outside of its limitations, therefore time has a definite beginning. You could say God was eternal before time existed, but what do words like “eternal” and “before” mean if time does not exist? Our perception is far too limited to conceive these ideas and speak about them in a rational or sensible way.