It's years since l enjoy myself so much.since可否换成before?

不能换.原句enjoy应该是过去时吧?since引导的句子可以看做是一个时间点,it's years=It's been years,从since引导的句子所发生的时间开始,已经过好几年了.其实意思就是我已经好几年没开心过了.但是,相似的结构里before可用," It may be many years before we meet again."直译就是是"在我们见面之前,还要过好几年",也就是,"我们得过好几年才能再见面".