Tony is correct, people often do not know year of the tractor.
ZB replaced the Z series in 1953. Z series had low seat platform and a hand clutch. ZB had a higher seat platform and foot clutch.
Engine serial plate should be on left side of engine (side opposite the starter). Tractor serial number should be on a plate on transmission case near the belt pulley.
Tractor plate should have 3 letters for model. ZBU, ZBE, or ZBN. ZB is tractor, U is Universal or dual wheel narrow front end, E is Extended or adjustable wide front end, and N is a single wheel front.
If you can get a serial # we can find the year.