Don't you guys read your manuals?
It's not a syncrho problem. Subaru intentionally made it that way to protect the engine. If you were driving at even 30-40 and put into first gear, it's a lot of work for the engine to match up the speed. I am not sure what RPM it should be in first gear at 30mph, but if it goes above 7-8k or higher, there's a chance you will get a blown engine.
If you were even at 10mph, it won't allow you to shift to 1st unless you double clutch. If you just forcefullly shift into first, it will break the syncrho, and that's when you take it to the dealer.
If you really need to shift to 1st when moving, put the gear in neutral with the clutch engaged, blip the throttle so the rpm reaches where it should be in first gear at the speed you are travelling and then change it to first gear, it will go in. It's called double clutching.