Older than my twin

Question: Two brothers are twins. One twin says he is older than the other. The other twin is confused and says: in order for us to be twins we have to born on the same day. How is the one twin older than the other?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: During what month do people sleep the least?

Question: When is 99 more than 100?

Question: What can be broken but never forgotten?

Question: Surrounded by life , yet life is its biggest enemy. But without life there is no need for it to exist. What is it?