I was in that situation about ten years ago, when I started. I know how you feel. By now I am on the other side and have trained a couple of Azubis (apprentices) full time until they were done, and also had some that get rotated through departments on a three month basis.
If your Ausbilder (the guy responsible for the apprentices) is not the right kind of technical person, treat him as your people manager. He is your boss, yes. But he can delegate. Typically individual lessons (Ausbildungseinheiten) that are based on the targets (Groblernziele) set in the document that describes the apprenticeship (Ausbildungsrahmenplan, Ausbildungsordnung) are done by individual people, not by the Ausbilder. In IT, that's hard. Especially because in smaller companies, people are busy.
Make sure the Ausbilder is actively delegating. Ask him to assign a dev who is responsible for you. Ask the devs directly for someone who would like to mentor you more.
If you are productive, and you get stuff done, and your stuff works, that's a great start. If no-one complains, that a good sign. Germans like complaining. If you would suck, they would tell you. But if you get stuff done on time, or faster, and if you have time to sit around and earn internet points on Stack Exchange and still get everything done on time, you are doing a lot of things right. (Maybe not the hanging out here part, you could always find more stuff to do :)).
If there are different Azubis or other people your age, talk to them about this. Even if they are more sales-oriented or if they is someone training to be a Buerokauffrau. They might experience the same thing. They relate. Talk to them. Together stuff is easier.
At school, talk to your friends. Ask them about their Ausbilder. Find one that has a very good relationship with theirs. Maybe their Ausbilder is only a few years older. Try to meet them. If their company culture encourages barbecues, going for drinks after work or stuff like that, ask your friend to be taken along. Then discuss your situation with the cool Ausbilder. They will listen, they will be sympathetic. They will probably offer advice, or offer to look at your code and tell you what they thing. I would offer that, anyway.
Contributing to Open Source has been mentioned, and you do that, here. But your technology stack is not ideal for OSS. That makes it harder to do that. But there might still be meetups for some of the technologies that you deal with at work. If you're in Berlin, Hamburg, Frankfurt or Munich, there will be some. Go there. Don't be afraid to talk to strangers. The people that go to those events are interested in technology, but also in meeting people. They will see you as a curious human being who wants to learn and not as a kid that doesn't know stuff yet.
I looked at your SO profile. You've been around there for a little bit over a year. You collected over 5000 internet points. You have a tag badge in C. You contribute to an automated system that helps keep the entire plattform spam-free. Your posts are concise, clearly structured, technically sound (as far as I can tell) and are usually well-received. Your command of written English is impressive for the average Azubi. Out of over 250 questions, only two have a negative score and you have enough integrity not to delete them. And I bet you probably are one of the guys helping the weak students at school, and maybe you are either Klassensprecher if that exists, or you're part of the Schülervertretung in school. I wish I had more Azubis that curious, motivated and nerdy. Keep up the good work. :)