>>length of time the buisness has been in operation<<
The only honest response is that you do not know whether the client has EVER been in business. You can't even guarantee that the IRS would agree he is self-employed, and you sure don't know what the bank's underwriting standards are, so why would you allow them to base lending decisions on YOUR signature? Simply say that you have prepared and e-filed tax returns which include Schedule C, the form normally used to report self-employment income. Period.