My research task is to delve into Irish indigenous wisdom and find any evidence of practices, concepts, rituals etc that society, at particular times in Irish history, offered to young makes to assist them transition / transform to adult manhood in a healthy manner.
There doesn't seem to be much information on the topic. This fact doesn't mean that no such rites existed. It could be that the traditions simply didn't make it into the history books.
There are a few history forums that essentially ask the same question, and the answers are limited, pointing out the issue with the history of the region largely being written by Roman scholars: https://historum.com/threads/celtic-coming-of-age-rites.42298/
The only thing that I could perhaps think of doing is surveying various rites of passage throughout modern day descendants, try to pull out anything that is obviously foreign, and see if there is anything that remains, but that would be a major guessing game.
You're quite welcome. I'm sorry that I couldn't provide a more detailed answer that included some specifics of rites of passage.