Is mowing neighborhood lawns, babysitting and working the family farm included in that graph? That’s what many teens did in the 50s and 60s.
Mowing neighborhood lawns is done mainly by immigrants nowadays. Anecdotal evidence is that this is true in many parts of the country, not just states adjacent to Mexico.
My younger kid has had a lawn biz since he was 10. Both my kids also paid for their own cars.