it was --(until/ when) he was 11 that his talent for writing

选WHEN
这是个强调句,不缺成分,去掉IT WAS THAT,还原句子,很清楚的．还原一下UNTIL,是错的．
但NOT UNTIL是可以的,It's not until.that.
这是个固定句型,直到．．．才．．．．
这里是可以的．