I'm just going to throw this in real quick because my comment has nothing to do with helping the kid out and it should.
These guys are completely right on the business aspects of lawn care so listen to them. Set yourself up and be legit you need to remember (especially with the economy today) lawn maintenance is a luxory so treat your customers like they are getting what they pay for. It's a cheap and easy business to get into so don't be like the guy who mows lawns illegally because he still gets a SSI check and want to make an extra buck.
1. Get an EIN
2. Insurance (GL 1 million is plenty)
3. Come up with a name and register it with the state (be sure to check on sales tax)
If your 14 and thinking about a business your smart enough that you don't need anyone to hold your hand and tell you what to do, however you do those three things and you've got the majority of the market beat.
Where do you get a commercial grade mower for $300 and if it's from Walmart you need to think your strategy a bit better.
FYI I paid around $800 for my 21" Toro, just a thought