I think "ice age" refers to being frozen in time so to speak. He is reminiscing about when they were both younger and how it can carry on, as they are both still in love with one another. The beginning of the song refers to new beginnings- "knocking down old Hollywood". It almost seems to me as though this couple is old and one or possibly both are dying. The summer years part sounds like an afterlife, in which everything is great again- "When their playing our song". The part where he is saying "I want to go back" suggests that he is still alive while his significant other isn't. It's an incredibly bittersweet song.
I think "ice age" refers to being frozen in time so to speak. He is reminiscing about when they were both younger and how it can carry on, as they are both still in love with one another. The beginning of the song refers to new beginnings- "knocking down old Hollywood". It almost seems to me as though this couple is old and one or possibly both are dying. The summer years part sounds like an afterlife, in which everything is great again- "When their playing our song". The part where he is saying "I want to go back" suggests that he is still alive while his significant other isn't. It's an incredibly bittersweet song.