I've had a major anxiety disorder since I was a child. My hair began greying when I was (happily) pregnant with my second child, my son. I was 25. It became more and more grey over the years until it has become purely white. It's still as thick as ever, though. Now I put a toner on it that makes it a creamy blonde-white. The goal being to keep it from yellowing.
In my case, it could be stress, but it could also be genetics. My father was grey by his mid-20's. My son is now 33 and is quickly greying.
I miss my darker hair, but nothing I can do, so I keep it toned.
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