The American constitution is the oldest one in the world right or not?

It isn't. San Marino created their constitution in 1600 although I believe it wasn't finally ratified till 1974. , The English colony of Connecticut formed theirs in 1638, though it fell out of use. Sweden and Corsica also formed constitutions before the US, although neither are still in use. It might be argued that the US constitution is the oldest still in use today, but it most certainly is not the oldest one created.