I am in my twenties and work 23 hours a week as standard but I often work a couple of extra hours in the evenings each week too and sometimes more. This week I will be working about 29 hours I think.
I do have two small children though. I worked 37.5 hours before I had my first child.
DH also in his twenties works 30 hours a week. Although does a couple of hours evening work on top most weeks too, but this isn't paid.