The normal retirement age on the Single Scheme for most members is the State Pension Age, which is 66 right now. If your job allows, you can keep working and defer your retirement to age 70. Or go earlier than 66.
If memory serves, I think that in 2021 the expectation was that the State Pension Age would be pushed out to 68 over time, but this plan got shelved at the last minute. So this may be why the AVC shows 68.
In any event you will be drawing down your AVCs at the same time as you retire from your job and draw your benefits from the Single Scheme, whether than be 66 or some other age. My cynical nature suggests that you e-mail your broker and ask them to confirm that there's no charge, penalty or financial implication of any sort for retiring your AVCs at an age earlier than 68.