How old does the Englishman say the alchemist is? How has he come to be that old?

The Englishman is obsessed with alchemy. The text tells readers that he spent most of his father's fortune in pursuit of learning the secrets of that mysterious art. In one of the textbooks about alchemy and the Philosopher's Stone, the Englishman read about a very old and knowledgeable alchemist. The alchemist is supposedly more than two hundred years old.  

He had spent enormous amounts of time at the great libraries of the world, and...

The Englishman is obsessed with alchemy. The text tells readers that he spent most of his father's fortune in pursuit of learning the secrets of that mysterious art. In one of the textbooks about alchemy and the Philosopher's Stone, the Englishman read about a very old and knowledgeable alchemist. The alchemist is supposedly more than two hundred years old.  

He had spent enormous amounts of time at the great libraries of the world, and had purchased all the rarest and most important volumes on alchemy. In one he had read that, many years ago, a famous Arabian alchemist had visited Europe. It was said that he was more than two hundred years old, and that he had discovered the Philosopher's Stone and the Elixir of Life.

The text is not more specific than "more than two hundred years old," unfortunately.

It's important for him to be that old though, because it guarantees that people consider him wise. "With age comes wisdom" is what people say, so being more than two hundred years old gives a lot of wisdom-building years. His age also gives him credibility. It is rumored that he found the Elixir of Life. Combine that with his age, and a person would definitely believe that the alchemist indeed must have found it.