We are His disciples if we do what He commands us. That is what our Lord Jesus Christ told us. He said that all those who called him Lord, Lord will enter His kingdom. In other words, it is not all those who call themselves His disciples are actually His disciples. It is those who do His commandments.
The disciples are not only the 12 apostles. The 12 apostles were just the pioneer disciples. They were the one who walked with the Master from street to street. They were those who witnessed the manifestations of His power and glory. They were there when He ruled the world with such a demonstration of authority that even demons trembled before Him. The 12 apostles were true eyewitnesses of His majesty.
We are His disciples if we listen to the doctrines which the apostles have laid down for us and obey them. If we live our lives according to His commandments, we also are His disciples. True disciples are those who obey the Master in totality. They are those who live after the instructions of the Master. We should live our lives according to the instructions of the master.