1) I did not realize Purdy was still only 21, I had it in my head he was an older senior; my apolologies
2) Age DOES factor into a player's future potential in the NFL:
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This is only for first round picks, but certainly an indicator that younger players have room more room for growth.
As noted above, I didn't realize Purdy was still only 21, so you can ignore the age part.
Seems like a selection bias at work more than an indication of age. I would be interested in the median instead of the average.