Since I was 14 years old. In Australia it’s normal culture to start your first job at age 14, or at latest 15 years old working in retail or fast food afterschool and on weekends and school holidays (everyone that works in these places is aged 14-19 except senior managers). I worked since the day I turned 14 at 2-3 jobs during middle school and high school at McDonalds, folding & delivering newspapers, teaching swimming, as a receptionist and as a research assistant at my future University.
During University I worked as a maths/chemistry/italian tutor, as a swimming/lifesaving instructor, as a temp receptionist, as an officer on a ship, as an ESL teacher, as a heritage building caretaker, created custom databases for tax accountants, as a sports teacher and youth counsellor at summer camps and at Blockbuster (it’s a DVD hire store – they existed pre-Netflix/broadband).
I’ve been working as a professional engineer for about 10 years (about 5 in Control Systems and Mining and about 5 as a Space Engineer with the ISS)