Today my 1 year old dog just started attacking my 7 month old dog. They did fine up until this morning. Now I have to keep them in separate rooms and if I let them in the same room, the older dog aggresively goes straight for the younger one and a barking, growling fight ensues. Why could this be? Neither of them are neutered. Would that help?

My first question was going to be if they're neutered.

Yes, neutering would help.