Figures suggest half of us go grey by 50 but millions start the transition to silver fox, like screen idol George Clooney, years or even decades earlier.
The study says the reasons are not clear but the stress hormone cortisol or mental health medications can cause damaging scalp inflammation.
A King Saud University team in Saudi Arabia compared rates of greying among 1,193 people aged 18 to 29.
Half had found at least one grey hair in their 20s.
One in eight reckoned they had more than 100.
Anxiety increased chances 2.24 times and depression by 2.56.
Family history of it was the biggest factor.
Smoking almost doubled the risk but good diet cut it by 32 per cent.
Study author Turki Albinhar said: “Lifestyle changes such as quitting smoking, a balanced diet, and managing stress can help mitigate risk.â€â€Šâ€Šâ€Šâ€Šâ€Š