Rabbit male dead (4 months old), she lives, should we buy a younger male? And would it fit if you are older? She is quite gentle and not aggressive at all ...
They should be about the same age but small differences are not bad either.
Please do not buy rabbits from zoohandlungen - they are deadly ill! Never buy a rabbit that is younger than 12 weeks! It's better, the babies were up to 14.-16. Week at the mother.
Please read how a socialization works. Otherwise it can happen that the two do not understand or even bad injured: https://www.kaninchenwiese.de/soziales/abrauf-he-vergesuranceung/