I need to find the age of this Miller Gas Furnace the serial# is MGH9607-01785
Well, please do not quote me but it appears it May be a Miller aka Nordyne. This leads me to think #MGH9607-01785 is around 1996. Possibly July 1996 (9607). It may help if you would have supplied the model number as well. May want to confirm with the manufacturer.
Do you have a model number?