It really has not changed that much. QB's still reach their peak around 3-5 years in. I have not looked but plenty of rookies started in the 80 and 90's and several QBs in "Todays" era do not start right away. It has nothing to do with being ready and more to do with team philosophy. I would bet most rookie QB drafted in the top 10 in the 80's started as rookies.