With a bit of online jiggery-pokery, I was able to establish that Ryan Stepp is 33 years old at the moment, so he was born sometime after 11 August 1980 and before 3 December 1980 (if indeed Ryan Stepp was 15 at the time of his goal v Taiwan).
This gives a range of 15y 250d-15y 365d (1996 was a leap year)
Given the information above, Allan Cole is the youngest player.
I haven't been able to confirm whether Ryan Stepp did indeed play (or score) vs Taiwan though. But I haven't tried very hard. The only place it's written is on Wikipedia in a rather untidy sentence. I only have one lineup for Guam in that tournament, vs South Korea, and neither of the two goal-scorers (vs Taiwan) are included in that lineup, unless the names given are incomplete.
Maybe Guam has had more young players/scorers in addition to those mentioned above.
Likewise I haven't been able to confirm for sure whether Allan Cole did actually play in 1966 in Puerto Rico. He was certainly in the squad, and reports afterwards mentioned that the team sustained many injuries and had to take to the field with some injured players. So surely he would have played.
He might even have scored, in the 4-0 win vs Puerto Rico, but I don't have the scorers for that game. He was also in the squad for CONCACAF 1967 but he didn't score.
I suspect there would be other candidates from teams in the Leeward, Windward, or South Pacific Games, but info simply isn't available.
The first goal I can find for Fofana was on 28-Sep-1983 vs Togo, at which time he was 17y 64d. But there are many unknown goals between his debut and that game.