Be patient, he will get it some day, it just takes time and being in the apartment does have it's challenges. They will have their little accidents even when they get older, just not as frequent. Having him neutered will not help with this but will help with the marking if he ever does. But I doubt he is marking at this young age. My Buddy boy is 3 years old and still intact and has never marked in the house. I would just take him our more frequently and just watch him. This will all be passed you one day, just be patient.