cuaiztaya.

Headword: 
cuaiztaya.
Principal English Translation: 

for the hair on one's head to be or turn white/gray; to become gray-haired
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 230.

Orthographic Variants: 
quaiztaya
Alonso de Molina: 

quaiztaya. ni. (pret. oniquaiztayac vel. oniquaiztaz.) encanecer, o tornarse cano dela cabeza.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 84r. col. 2. Thanks to Joe Campbell for providing the transcription.

Lockhart’s Nahuatl as Written: 

ni. Class 1 or 2: ōniquāiztayac or ōniquāiztaz. quāitl, iztaya to whiten. 230