valkyrie question..

She was born earlier, but weren't there indications that time works oddly on the trash planet?

She is significantly older indeed.

When Hela returned to Asgard, she angrily remarked, “Doesn’t anyone remember me?”

And that’s because no one in Asgard actually did. Odin had basically erased her from history, so the Asgardians didn’t grow up hearing about her at all (Thor & Loki obviously knew nothing about her). As such, Valkyrie must be a few thousand years older than Thor.

And remember, the film states pretty clearly that time moves differently (much slower or faster) in Saakar. I assume Valkyrie landed on that planet shortly after she fought Hela.