depends what you mean by "proper"
Aged 8 I got money from helping my sister on her paper-round, but that was money that was already part of the household...
I actively brought in money by singing for weddings when I was 10, and ringing for weddings when I was 12 (these were the days when the choice was church or register office, so for most of the summer there'd be 5 weddings every Saturday).
Paper-round at 13, and baby-sitting at 14.
Obsolete Archive checker (ie make sure there was nothing there that shouldn't be thrown away) at a solicitor's for a few months during 6th-form (my mother was their filing clerk. I got £5 from the petty cash for a short morning's work).
Admin assistant to a dealer in niche collectables - ad hoc during 6th form and then full-time for 9 months.
Summer chambermaid in Bavaria age 21
Summer chambermaid in York (my uni town) age 22
Temp with an agency from 23 - factory, cleaning, office