i have some questions

I want to get some opinions on aging BT's... my Sky King is 7 and he started going gray a year and a half ago or so... and its getting increasingly worse (not too traumatic seeing I started going gray at 27) i was just wondering what kind of longevity others have had with their BT's. Is it unusual for a 6 YO BT to start graying? (so far its mostly on his muzzle but he has a few stray hairs on his back and hind legs as well)