Any kid finding customers willing to pay $25 to mow an average lawn doesn't need an allowance. :-)
Then again, I expect the kid might be persuasive to some homeowners who have already looked at professional lawn care companies and found the going rate more like $50+/hr.
Most babysitters are the same way these days -- whereas apparently a generation or two ago the money was mostly a formality (often just a couple bucks per hour!) and you babysat largely as a favor to others, these days most would-be babysitters are going to charge you at least $10/hr... after all, they could make about that much flipping burgers.
Or something like that.
:-)
---Joel