Which is correct:
1-His birthday is not for two months.
2-His birthday is not for another two months.
3-His birthday is not till two months.
4-His birthday is not before two months.
I think '1' and '2' work. I am not sure about the other two.
You're right. 3 and 4 don't work.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.