Wow...I honestly thought everyone had at least some gray hair by their 50s (and most during their 40s as well). You are a rare and lucky person! I got my first couple of grays at 25. I'd say I'm about 50% gray now at age 50.
I have a couple of stripes, maybe a 1/4 an inch wide above my temples, but not a lot of gray (yet) at age 50. Seems to be genetic, my mom is 76 and still has naturally blond hair with just a bit of white streaking through it.