I adopted a 10 year old cat six months ago and then got a 7 month old cat a couple days ago and they do not get along.

The 10 year old is a female and the 7 month old is a male and much much bigger, shes always been super scared and anxious, but shes way worse with him here. He will just go over and hiss at her and bully her for no reason, he is super sweet to me. Does it just take time?

Another question is, shes 10 and spayed but hes 7 months and un-neutered, has his claws. Will he try and mate her? Would that hurt her?