Well it doesn't mean three months ago was the LAST time he washed his hair...
Is there a difference between 감다 and 씻다? Is 감다 only used for hair? I know that 감다 can also mean to blink (your eyes).
You could use 씻다, but it is not natural to say 머리를 씻다. Memorize it as 머리를 감다 as an expression. 감다 Usually involves something thin and long like hair, where as 씻다 involves some type of flat surfaces.
감았다 doesnt apply here...
Can you explain why not?
감았다 is also a correct answer
It must be really dirty than
So I think the man's hair had become nest
Can "삼 월 전에" be used here?
No. 3월 [삼월] means March. 삼개월 Is three months.