The antonyms for the word 'most old timer' would be some of the following words: newest, latest, modern, contemporary, young, fresh, current, present-day, recent, up-to-date, and current. While the term old timer is usually used to refer to someone who has been around for a long time, the antonyms imply the opposite. For instance, newest refers to something that has been around for only a short time, while modern implies the use of up-to-date technology, something contemporary is relevant to the present time, and young implies that something has not been around for long. Therefore, these antonyms of old timer connote the opposite meaning of the term.