你可以理解为 longer 后面省略了相关名词。但这样理解的话，前面需要加上冠词，比如说成 I didn't have a much longer life to live。又如：

I should go mad if I had to spend any longer in this place. 如果我在这个地方再呆上一会儿我会发疯的。

A skilled worker does his work quickly while an unskilled worker will spend much longer (time). 熟练的工人会迅速地把工作做完，而不熟练的工人要花好多时间。