I'm pretty sure it was Clint Marcell. He was 15 and his debut was vs. Sweden. I believe in 1984.
Flex, your second question is a bit ambiguous. What the hell is a tender age.
I believe Gally was 16 when he made his debut.
I have a feeling if you talking about any others at a "tender age" it go be the youths from St. Benedicts back in the 60s.
VB