In terms of the law
, I do not think a the relationship of guardian is accepted relative to dogs. This is not downplaying your feelings on how the dog-human relationship should be but that the law considers us as dog owners
and fully accountable for their actions. A guardian is someone appointed by a court to care for another human being incapable of caring for themselves.
Unless there were breed specific bans (which can be legal) just having a dog of a certain breed would not be cause for legal action.
It is an unusual question. Is there more information to put it in context.
In terms of you being a dog-walker, I would definitely talk with an attorney concerning your liability if something were to happen with one of your client's dogs while you were in control of it. It would be money well spent. You may want to consider a liability policy and could sign legal documents now that you are 18. I would most assuredly have a contract with your clients and any licenses required by the state/municipality.
Some AVMA information about legal status-not sure if it is relevant but it is a good read.