hey i'm 15 years old and me and my brother have a lawn mowing business too. But we only have 15 customers. We just bought a brand new Exmark Metro 36" so that's going to help a lot. We mow in the evenings so we are pretty busy. Go for a commercial walk behind. Get a used that is in good condition and try to get a decent price. Actually price probably wouldn't matter b/c you got 60 lawns and that should be paid off in a month definitely. Get a good trimmer soon. we have a Stihl and it's awesome but i want to get an Echo. Also, do you not go to school? Do you just mow all day and that's like your job? Do you have a worker?