I don't know Eminem's songs, but 25 to life usually means the time a person will be in prison. When someone is in court and is guilty, the judge will sentence him. The sentence can be "25 to life." The person can get fro 25 years to the rest of his life in jail. The judge decides. You can say "That crime carries a sentence of 25 to life." "You can get 10 to15 for committing that crime."