he has been there for five six mouths

首先,是months,不是mouths(嘴巴)
第一人称有单复数单数 单数用I 复数用We,不过后面都加 Have
如果你说是是5或六个月,应该是five or six months
如果你说的是五个月零六天应该是 five months and six days
所以上述表达有问题.
Have been in +地点,不过不算是句型