On the other hand, you ought to be able to honest with your sensei. And you can always phrase it as a statement rather than a request--"I'm uncomfortable testing so soon" instead of "Can we revisit this decision in a year?" Six months is not a lot of time even with constant, regular practice which is something that cuts two ways. If you're really not ready now you wont be then either. But your sensei isn't likely to be expecting too much change out of you so chances are you are far better than you think. Ask for a pre-test in October and have somebody video it. Then you'll know for sure.