もちろん、誰も確かではありませんが、教育を受けた推測をしました！4543億年は、今日の最良の見積もりです！また、あなたは文法が間違っていたと思います。あなたが書いたものではなく、「地球は何歳であるか」を意味したと思います。
Well, no-one know's for sure, of course, but we have made some educated guesses! 4.543 billion years is the best estimate we have today! Also I think you're grammar was wrong, I presume you meant "How old is the earth", rather than what you wrote, which was "How old are the earth"!