Now this is as far as I know and NOT OFFICIAL....
But the Pro League is not that old, and my answer is based on what I know, so feel free to correct me.
Question
1. Who was the youngest player to play for a Professional Pro League club's Senior team.
Bonus Points.
1. The Club he made his appearance for and against whom.
2. In what type of competition (Pro League, Pro Bowl, FA Cup, etc).
3. How old was the player.