Mistake or Sin?

Making mistakes is a central concept to coming-of-age. Letting adolescents make mistakes is often seen as necessary for growth and maturation. In A Portrait of the Artist as a Young Man, Stephen believes he is eternally damned for his indulgence in sin. However, this brings up the question whether Stephen's sin is an adolescent mistake or actual sin. He seems not yet old enough to be damned for life but his actions are, as he says, "mortal sin". How far can young adults go for mistakes to stop be considered life lessons? In our own system, minors aren't tried for crimes the same way adults are. Unlike this, Stephen seems to think he would be judged the same way as an adult in the eyes of God for his sin. 

This thread of thought connects to the question of why certain ages turn adolescents into adults so suddenly. At age 18 in the US, people are immediately adults and thus their "mistakes" are considered crimes. Although I'm not sure of the rules in late 19th Century Ireland, Stephen seems to think he should be judged before God like an adult. In our customs I think Stephen would be judged as an adolescent because of the age he is. However his self-entitlement as being more mature or special than others his age seems to be part of the reason he judges himself as an adult.