Is my brother allowed to saturn?

My brother 14 years has saved 400 euro, now he wants to buy an xbox. But our mother says she does not order him on the internet, but she agrees to buy one in the saturn / mediamarkt. As he goes to the strietzelmarkt in dresden with friends next week. Did he want to buy one for saturn? But he should not buy any yet. Or if our mother writes him a power of attorney can he buy one?

But. He has limited legal capacity and can buy with his pocket money (pocket money paragraph)

It may be that he gets in trouble, because 400 euro are still a lot of money and since a 14-year-old can't conclude a contract, it can happen that the cashier no longer runs the 400 euro under the "pocket money" section.

The best thing is nuts goes with it.

The mother could come too, then you are definitely on the safe side, if there are problems with the purchase because of the age.