Hmmmm
Good advice if you want to be in the lawn mowing business. I could be wrong but I suspect that for your next couple of years your main job is going to be school followed by college. I'd concentrate on that if I were you.
Going by my own experience as a teenager, (I caddied one summer at a golf course, washed dishes at a summer resort the next year, waited table at a summer resort after that - great money, worked as a house painter for my dad one summer - could have taken over the business and spent one summer doing mostly lawn mowing and other odd jobs) I didn't end up doing any of them for a living even though a couple of them worked for other people, one of my waiter buddies did that all his working life and loved it.
One other thing that has not been mentioned. At least in Delaware, lawn mowing is a highly competitive business. If there are a lot of retirees in your area, you'd be amazed at how many of them will take on lawn mowing jobs (at least until they get that John Deere D100 paid for) and as fast as one gives it up another steps in.