很高兴能够在这里回答你的问题：
He started to learn English when he was 12 years old.(保持原句意思）
He （didn't）start to learn English (untill) he was 12 years old
not untill 句型
2.Without rain,the living things will be all dead.(保持原句意思)
If （there is）no rain ,the living things will be all dead