14, bussing tables and washing dishes at a restaurant, ushering and working concession at a live theatre, painting and cleaning at a commercial site, nannying up to 30 hours per week (40+ in summer holidays)
12, babysitting
before that, commercial yard maintenance contract with my dad and siblings
before that, paper route
A variation on this question was in YMOYL, and proved life changing for me: Around age 22 I developed a severe disability. I applied to the federal disability pension plan and was told I hadn't had enough work hours to qualify, even though I had been doing professional (albeit low-paying) work for some time by then. When a short time later I answered this q in YMOYL, I thought, "Wait, I've worked loads and loads since I was a kid. The plan people can't be right." I called them up and said so. They checked again, sent me a large lump sum and started sending me monthly cheques!
I don't know what hours/work they deem "official". Much of my adult-life work has been part-time, weird, low-paying, contract, self-employment, etc. I've only had two years of income high enough to pay taxes!