This. I added a 2nd male to my house, an 8 week old pup with a 22 month old male. They are now 10 months and 2.5. I keep a close eye for changes. So far so good, but when I got that pup I knew that there was a good chance I may have to crate and rotate eventually. Mentally prepared for it. My friend has 2 males intact from same and similar lines. They get along, but again it was an 8 week old introduced to an adult, carefully and slowly, by a handler who knows what is what. Decks stacked in favor of. But still no guarantee.I think Leerburg has some information about introducing a new dog to a resident dog that may be helpful for you to read. I would take things slow and crate and rotate the two dogs for now. If this is a long-term living arragnment, hiring a qualified GSD-experienced trainer would be wise. I have two male GSDs. Although things started out well, when the younger dog turned eight-months-old or so, they started having altercations. I keep them seperate at all times. If one dog is upstairs, the other is downstairs, or outside, ect.
When they are both over 2.5 without any signs of impending real fights, I'll start to be truly optimistic.
Lots of non negotiable ground rules. Separate feeding, alone time with each (I give crate period times to each so they have a break from each other), they are not allowed to play rough. If I have them both out they are pretty much focused on me. I have seen some jockeying for my attention and that is usually my cue to put one up and play it out with them one at a time. It's work. But without that foundation and work, odds are stacked against you with same sex pairs.