Diagon Alley, a street in London, was one of the first trails of magic known. It is concealed by a magic brick wall behind an inn called the Leaky Cauldron.

No one knows exactly when Diagon Alley it was built, but one oldest shops known in it is called Ollivanders. Ollivanders is a family company of wand making, founded by Garrick Ollivander. It is a small place, with wands lining the walls of the shops, each in a set coded order.

The shop was founded in 382BC, which it says on top of the little shop. It is still open even now, so many thousands of years later. It is also the most popular wand shop in Britain.

Though another shop was opened around the same time as Ollivanders, called Madam Malkins Robes for All Occasions, a robe store.

They supplied with many different robes for (, like the name suggests,) all different occasions, including formal, casual, and much more. They also have Hogwarts robes and, on a rare occasion, also stock Durmstrang and Beauxbatons robes.

People think that Madam Malkins robes were founded around the 380s era.

So knowing this information, we know that Diagon Alley has been open for very many years, and I expect it to be open for a long, because of how well the business is going.