Jein.

Yes, he can travel on his own.

NO-various countries, esp also Germany, set specific rules (these often come from overcautiousness etc - also cases of child-trade etc. for minors going abroad. This is far too specific and detailed to all write down here-plus its books full of law etc.

From 16 it becomes a lot easier in many cases-but still not as free as from 18.

Apart from the travelling itself, you need to verify that the accommodation will allow minors to stay without an accompanying adult. Many hostels only allow adults, i.e. 18+.

You also need to check what rules the different countries have for letting minors without parents cross the border.

https://europa.eu/youreurope/citizens/travel/entry-exit/travel-documents-minors/index_en.htm