since about six years 是错误的.
since 用于现在完成时中,后面跟过去的时间或者跟一般过去时的动作.
例如：
She has lived here since about six years ago.
=She has lived here since 2007.since for about six years正确吗？since for about six years是错误的。正确的说法是：since about six years ago或者是 for about six years