While I understand and mostly agree with your larger point (he's unlikely to be selected), I believe if added now, Kepler would be 24 when he "had" to stick in the majors. Ages 21-23 would be his three option years. From your list, it should be noted that Bartlett, Mientkiewicz, Koskie, and Jones were all college draftees. Those ages you list were generally their fourth full pro seasons, a level Kepler will be attaining next year (giving him a pass for his first "full" rookie ball season at age 17). Even if added to the 40-man now, Kepler would still be getting 6+ full seasons of minor league play. Also, Kubel only played 30 games in the minors after age 22, and probably only "needed" them due to injury. Morneau played 72 at age 23, arguably did not need them, and played none thereafter. Cuddyer played 55 at age 24, arguably did not need them, and played none thereafter. Guys who are capable of becoming MLB regulars are generally capable of sticking in the majors by age 23-24 (or, if college drafted, age 25).