Lions and tigers only kill and eat men when they are too old and

你的句子不完整.完整的句子应该是这样的：
Lions and tigers only kill and eat men when they have grown too old and too weak to catch their usual food,such as deer and other small animals.
这里的两个too分别用来修饰两个形容词old和weak,并且在中间用了连词and为什么不可以用两个too呢?
你是不是想说“为什么不可以省略一个too呢?”
答：用两个too来分别强调两个形容词,语气更强.这和汉语表达是类似的,我们会说：“太老,太虚弱了以至于.”我们不会说：“太老和虚弱”所以这个too不能省略.