I'm in my 20s, and due to a combination of crippling student debt and choosing to pursue my dream job in london, am still living in a rented flatshare with no escape in sight 
The classic issue- my flatmate is messy and avoids cleaning. She keeps her bedroom door shut, but once I had to let the landlord in and it was like a teenagers with crap everywhere and a musty smell. Obviously that's completely fine as it's her space, but as mess/dirt doesn't bother her I always end up cleaning in the communal spaces.
In the end I suggested each of us cleans half the flat once a week, it's tiny so honestly takes no more than 20 mins if you're fast. We've lived together for almost a year and recently every week there's an excuse- she's tired, she's too stressed, too busy, or recently, she was upset about the situation in a country she'd recently visited and didn't feel able to clean. I have such frustration as it's not like she's so busy she has no time- she doesn't work and is doing an artsy masters that takes up around 5-10 hours each week. The rest of the time she spends in coffee shops and restaurants.
I feel weird about talking to her about it as she's a grown woman at 38. What's a non-confrontational way to go about this? Would i be unreasonable to say if you don't want to clean that's fine, but please pay for a cleaner to do your portion? She takes absolutely ages to organise or sort out anything, so I could see her saying that's fine but never actually get round to organising it. AGH. Work is stressful and the house is gross! (DM is loving the situation as I used to be a messy teenager, much to her despair)