It is, of course, always possible to take an IQ test at an out-of-standardization age, but you won't be able to obtain genuine standard scores. Since this is for access purposes, this seems counterproductive, as you would both have invalid scores, and also lock yourself out of obtaining valid scores for another two years (on the only instrument the school accepts). If he misses the cutoff by just a few points, there will be no way of knowing if that was largely due to the difference in age of 3 months, as we're not comparing apples to apples.
I also think you may be placing your child at a disadvantage by having him test in his secondary language. Especially as, at this age, most vocabulary is obtained from environmental sources, for which he may or may not have the same richness currently as the norm group did. Just because he can read does not necessarily mean he has equal access to vocabulary. Of course, I assume this will be the language of instruction, so it may make some sense to see his level of function in that language (but you'll have to take the score with qualifications). And, naturally, all family factors need to be weighed in the decision.
