In my knowledge... Lasith Malinga of Sri Lanka is the youngest to get hattrick.
Sachin Tendulkar is the first and till now the only player to score a double century in ODI Cricket.
Lala Amarmnath was the first cricketer to score a Test century for the Indian cricket team.
Deandra Dottin of West Indies is the first woman to score a century in International T20 Cricket.
46 centuries in International Cricket