Dianne, my son mowed yards for several years till he was old enough to get a job (he got his first "real" job at 15 and still did a few mowing jobs then). He made great money doing it, too. It's a great business for teens.
Once he had enough to open a bank account, that helped him (a little) not to spend it all as soon as he had it. He could "save up" for bigger stuff. LOL
Your son learned valuable business lessons with his shoveling business and I'm sure he'll learn more with mowing. It's such a great intro into the world of customer service, collections, time management, and more!
Congrats to him for having the spirit of the entrepreneur!