^^ that. A Corso is very people oriented & no offense, it sounds like you're depriving him of that which means he's acting out by jumping on you or whatever else he's doing. He will thrive from human interaction & if you want him to be obedient sounds like you need to go back to the basics.
First of all he's young. If he's had no formal training before now then you need to look into establishing a training protocol with him. There are numerous threads on the forum talking about training & behavioral problems. I suggest starting there & seeing where the threads apply to your situation. If financially you can afford it, call a reputable trainer. I'm thinking you might need someone to help train you as well as him so that you have a better understanding to what his basic needs are as a mastiff. Find a trainer with mastiff experience. Mastiffs are not like most dogs. Corsi especially are very intelligent.
Like cway said above, mastiffs need to be with their people. I have a feeling you might have rushed into the decision of the dog (just my opinion) & you went for a dog you thought was going to protect your property & look the part too. Any dog will protect it's people & it's property if given enough mental support from it's owner. A Corso will do this naturally unless you got the dog from a not so reputable place & genetically he's not exactly a correct Corso. I'm not passing judgement whatsoever, so please don't take offense to what I say. I'm just trying to help the situation.
