>>3177148Datamined info from the PC benchmark. It contained some things from the Windows Edition/Royal Pack. From his dossier:
>Though he was chosen by the Crystal to serve as the savior of this star, an injury incurred as a young boy deprived him access to the full potential of his innate power.There are also some in-game conversations about it - turns out that Prompto (and maybe even Gladio) knew nothing about the real extent of issues and Noctis sure as hell wasn't about to tell them. He was supposed to be Armiger Unleashed tier even as a teenager, but wasn't because he's pretty much a highly functional cripple.
The Parting Ways mininovel touches on it too, when Noctis and Ignis reminisce about their past.