I know it may sound very young, but I was 6 when I first started mowing. I found an old weed eater and just started mowing along all on my own. My father had to show me how to start out but after that it was smooth sailing. Also I started mowing with a lawn tractor at 7. Then after that I loved using lawn equipment so much that I started to work on them. But I say overall, you should be 13 to start using lawn tools responsibly and in the correct way. Also I think you need supervision until this age.