age作为先行词的定语从句用什么关系词?
我阅读遇到这样的句子：
When she got to an age where she gained enough skill to go outside her garden, she asked her mother if she could go for a bike ride outside the gate and down the lane.
其中的定语从句为什么不用when?
问题补充：age应该指时间,却不用when
why?