House-sharing gets harder as you get older. The pool of people you can stand to live with shrinks as your friends start to couple up and move in together. You have a better idea of how you want to live, but you also realize that not everyone can give that to you, and you have far less energy for when disputes inevitably occur. 

There are however some things you can try in order to achieve domestic peace. The first is to get a cat. A pet gives even the most fractious housemates something to agree on: Your pet is the most beautiful and perfect creature on earth. It may be hard to believe now, but you will naturally come to feel this way about your own future feline.

Everyone has different levels of mess they can tolerate. A truly filthy housemate is not a viable prospect in your 30s, but...