I have heard several times over the years that stress is a big contributor to forgetfulness. It's based on the simple arithmetic of when our brains are busy juggling so many things at once, we can't stop and recall the little stuff, basic everyday things---too much of the brain is taken-up, and pre-occupied. I have noticed this in myself.

Insufficient sleep has also been noted as a possible contributor.

I don't know if it's "normal" or not for problems to show up in our 50's, because I was in the throes of some pretty powerful depression and anxiety, as well as the onset of a bad case of of hypothyroidism, from the age of 46. These 3 ailments pose big problems for both memory and cognitive function. But I have also noticed it starting to happen to my husband, who is very active and healthy, and whose memory has historically been as sharp as a tack.

I do much better with almost everything when I can find the discipline to eat right and exercise (giving the brain good food, and keeping it oxygenated). Mental exercise helps, too (reading, learning new things, games and puzzles, etc.)

This article outlines everything very well:Memory Problems: What is Normal Aging and What is Not?

Wishing you all the best with everything!