Dd is 21. Until this summer she was at university. Due to her course, and voluntary work experience she didn't do a paid job - so 0 hours.
When on placement she was working [unpaid as placement] full time 5 days a week - averaging around 40 hours a week, plus working at home for prep, etc.
She is working abroad this summer, paid though pretty much minimum wage, and doing around 30-35 hours a week. No permanent job to return to yet so who knows after that.
Her friends vary from 0 hours (full time university with placements so no paid employment really possible) to 40+ hours (full time paid employment) - all very early 20s.