Interesting.
The term itself is an oxymoron, but this person does genuinely seem to believe they have that identity. And if it allows them to conduct their lives in a way that makes them happy, able to feel comfortable with themselves, and harms no-one, who are we to judge?
I suspect that there may be other issues at play; maybe an underlying need to recapture youth, a desire to return to innocence, absolution of responsibility... but regardless, to each their own.

I find it curious that the identity is selective, though. Like... the person in that article has decided to untrain themselves in using the bathroom in an attempt to be more infantile, yet has kept the capacity for articulate, fluent speech and reasoning, and the right to freedom of choice... all of which don't fit with the identity expressed. Maybe those are things a person can't 'unlearn', or maybe doing so would make functioning within society almost impossible... in which case the identity is dependant on something outside the individual.
Still, the mind is an infinitely complex arena. Live and let live.