Alexs I have tried to make my password 5 numbers long and i cant find out a way
Most of our devices run Budgie, so Gnome may differ in this respect, but I was able to set a 5-character password for my wife, who's non-technical and has memory issues. At the point of installation I couldn't use the one password she can remember (the name of her cat), so I set it longer, just to move on from there.
Then, in a terminal, I used the passwd command to change it to the 5-character version she wanted. I had no problem doing it that way. It's not what I would have preferred, but her laptop never leaves the house.
And when mama ain't happy, ain't nobody happy!
