Binance, Gimi and Coinbase has minimum average purchase of bitcoin values at $1 to $5 which means there are possibilities for €10 purchase of bitcoin.
He is under 18 years old. He posted that on his
other topic.
But then, the level of his account is being considered. Let it be known conciously that procession of the the transaction requires charges which might the fraction the bitcoin purchase order.
There are many exchanges (both decentralized and centralized exchanges) that are having lightning network. He can first use lightning network to accumulate and later use bitcoin address instead.
I don't see the point of buying 10€ worth of Bitcoins, but if you want I can give it to you.