Untill what rating do openings not matter at all?

I've seen that when I don't use openings that I still win and even sometimes playing without an opening is better. Until what blitz rating should I not use an opening and just play for fun? I'm currently around 1050 blitz rating.

You have misunderstood that maxim. When you are a new player, you should focus on learning and using general principles of chess-  piece development, king safety and such-- rather than trying to memorize opening lines.

That doesn't mean that you should play random moves in the opening.

In blitz openings don't matter very much no matter what rating you are. Even players like Hikaru play gimmicky junk in blitz... and I don't mean once or twice, I mean almost exclusively. You'll never see him play a main line Najdorf, you'll never see him play a main line Spanish, etc. The only exception I've seen is sometimes vs other top players, and when money is on the line, he'll play some top of the line theory.