NFL starting QBs younger than Winston: Murray, Jackson, Jones, Darnold, Mahoney, Watson, J. Allen, Goff, Mayfield, Trubisky. (And K. Allen, Rudolph if you count them)
Alex Smith is an interesting model for delayed progress in TD/INT ratio. No. 1 overall pick, first five seasons he played, 37 TDs, 43 INT, never a TD/INT ratio better than 1.5. From there, 156 TDs, 58 INTs, had a TD/INT ratio of 2.0 or better in seven of last eight NFL seasons.