He wasn't a player as such when he acquired a new nationality, i.e. assuming he had already Irish nationality when he played for the u17's.
He acquired the Irish nationality before he became a player, while he was a minor.
That's how I read it.
The last line of Article 7 gives the biggest clue to that
'He has lived continuously for at least five years after reaching the age of 18 on the territory of the relevant Association.'
For example if a kid settles in Ireland at the age of 12 and acquires Irish nationality by the age of 15, he does not have to satisfy the requirements of article 7.