Becoming a mercenary through him is conditional: he tells you it requires obtaining 'something so important', which you then have to get hold of before you can join.
New Camp — Chapter 1: A mercenary you can ask about becoming a merc.
Items Torlof carries in Gothic 1 Remake.
368
Torlof can be found in the New Camp (Mercenary).
You: What's your story?
Torlof: Hmm. Makes sense, I guess. With all the bastards under this dome it's easy to forget what a normal conversation goes like.
Torlof: My name's Torlof - used to be a First Mate in the Royal Fleet.
Torlof: Let's just say, mutiny was involved, and it wasn't as successful as a mutiny should be.
Torlof: Now I'm here.
You: I want to become a merc.
Torlof: Good for you. Lee only takes the best of the best, though.
Torlof: 'Til that applies to you, you should go shake hands with Lares and his guys.
Torlof: If you want some advice: try and steal something important from the Old Camp or the Old Mine.
Torlof: That proves you're against Gomez, and that's half the deal.
You: And how should I get my hands on something so important?
Torlof: That's your job to figure out. If I was you, I'd try to win their trust first - then you rip 'em off.