The consensus seems to be that AJ never had what it would take to be in the mob, but by the end of the series he is only 18. Based on the few flashbacks of young Tony, it seems like AJ had seen just as much, if not more of the mob life. Sure, he never saw Tony cut off someone's finger, but he saw his father arrested, shot at and actually shot, and knew many family members who went to jail or were murdered or "disappeared." I'd also say, while based on limited evidence, AJ acted out more than young Tony, and in deeper and darker ways, such as attempted murder and suicide ( regardless of how serious those attempts may have been.) I think that it is entirely possible Tony was a fairly normal kid, considering his upbringing, and went away to college, but ultimately failed and returned home. By that point, the mob life was his best option. So if it's possible AJ was even more messed up as a child than Tony, his transition into the "family" after leaving the nest and failing in either college or the military (which based on his character seems entirely possible) seems certain.