“I did my time” Neil did his time (jail) during all the years spent under his father’s control. He did his time, he should be able to be happy and run away now, right?
In the original script, Mr Keating explains that becoming a full member of the Dead Poets Society required a lifetime of apprenticeship, and therefore, the only true members are dead. All the living members are simply pledges, including Keating himself.
So, of all the boys, Neil was the only one to become a true member of the Dead Poets Society.