If you are a Year 13 student taking papers at the University of Otago while at secondary school you will be deemed "eligible" for fees-free study. You will not have the option of "banking" your fees-free entitlement for a future year.
However, under current Government policy, if you enrol for less than 1.0 EFTS of fees-free study in 2020, you will have some remaining fees-free entitlement to use in future years. This remaining entitlement is called "carryover".
For example, if you enrol for 0.15 EFTS of fees-free study at Otago while at school in 2020, you would generally have 0.85 EFTS of carryover to use in 2021. Any additional EFTS consumption in 2021 would need to be paid for by you, via the Student Loan scheme or otherwise.
The information above does not apply to STAR-funded students at other New Zealand universities.