Maybe post the engine model and serials - those are more universally understood.

16hp v twin vangaurd 303777-1111-A1

these are the numbers on the motor.....model 303777.....type 1111-A1.......code 96120911

click the link to a thread where this was recently discussed.
According to the Date code # of the engine, the engine was built on December 9, 1996.
Assuming the engine was shipped shortly thereafter and installed in the tractor upon reaching the tractor plant........your tractor might be model year 1997.

Here is a link that might be useful: Don't lie about your age

Here's your manual for your mower: http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=heCyEN8ctF1rE3CG.54bp796Dq

Here is a link that might be useful: Agri Allis/Simplicity Owner's manual