Yeah, I'd say so. Doesn't matter how much you protect your hearing afterward, the damage is done. But it's not just hearing loss in itself that creates tinnitus, otherwise, everyone would have tinnitus, it's how your brain reacts to the loss of expected auditory input.
But I'd say if someone doesn't develop chronic tinnitus in their loud 20s and then they start protecting their hearing, their chances are definitely higher that they won't develop it than if they had continued to damage their hearing.