If males between the ages of 17 and 45 journey for longer than three months, they have to typically get hold of permission from the Bundeswehr. This is what the conscription legislation has mentioned for the reason that starting of the yr.
https://www.spiegel.de/politik/deutschland/wehrpflicht-maenner-bis-45-muessen-laengere-auslandsaufenthalte-genehmigen-lassen-a-75dadcaa-967e-48be-abf9-bcd1000c0fd4#ref=rss