If you're doing a masters does your uni not have halls exclusively for postgraduates? If so, a significant proportion of your flatmates will also be 25+. I don't think at your age it's a good idea to move in with 18/19/20 year olds as you would probably find them a nightmare to live with.
Think about it, they have only just become legal adults and will likely be going bat$hit crazy on booze, sex, drugs and every other worldly sin. At the same time, you will be trying to study.
You'll probably have no common ground with them whatsoever.