“which in the life innumerable suddenly lively and desolate ”是修饰maturity的!这是一个定语从句.
如果你是想表达这样的意思“也许一个人要走很长的路,经历(体验)过生命中无数突如其来的繁华和苍凉,（然后）才会变得成熟.”的话,你可以把它改为：
Perhaps a person needs to take the very long road and experience innumerable lively and desolate things that happen suddenly in the life,then he may grow into the maturity.
如果语气强烈且肯定,可用not……until结构：
A person does not grow into the maturity until he needs to take the very long road and experience innumerable lively and desolate things that happen suddenly in the life.