You and Your Hair
undo their plaited hair (for ghusl). She observed, "It is amazing that Ibn 'Amr orders women to undo their plaited hair for ghusl. Why doesn't he just order them to shave their heads? I and the Messenger of Allah (peace be upon him) used to bathe from one vessel, and all I did was pour three handfuls of water over my head." (Ahmad and Muslim)
With regards to gray hair, it is a blessing for anyone Muslim. 'Amr ibn Shu'aib related on the authority of his father from his grandfather that the Prophet (may the peace and blessings of Allah be upon him) said, "Do not pluck gray hairs as they are a Muslim's light. Never a Muslim grows gray in Islam except that Allah writes for him, due to that, a good deed, and he raises him a degree. And He erases for him, due to that, one of his sins." (Abu Dawud, Ahmad, Tirmidhi, an-Nasa'i, Ibn Majah)
* Muslims always ask for the peace and blessings of Allah to be upon the Prophet Muhammed when mentioning his name. Read more about that here.