If it has a briggs motor, the 1st two numbers in the code are the year of the motor- if its an original motor to the tractor, then that will be in the ballpark for its date of manufacture.
Most MTD's from the 90's all use basically the same chassis /driveline ( LT's - GT's are heavy duty) - i own several LT's from the 90's - i do have a couple 80's MTDs with the step thru chassis and a 2003 bolens - the bolens chassis is way different then the basic MTD chassis.