Simply a Rose to brighten your day,
And maybe lessen the cares in your way;
And also, too, to help you to know,
That in knowing you, many others grow!
I think you would have to be at least 18 because that is usually the age at which you can contract or make legal decisions.
If you are talking about a specific individual, you would have to get them to give you a limited power of attorney that authorizes you to act on their behalf concerning their financial affairs.