Was Shogun artificially aged?
As seen in the anime (carefull this contains spoilers). 


   Towards the ending shogun reveals that he actual is Takumi Nishijo His original. and the main protagonist was just a fantasy of him. In this part he also reveals that he has a rare disease which causes him to age when he uses his power (believe this information is given spread over episodes 10-12). They do not go into details about how he got this disease


With this the answer to your question would be No, Shogun was not artificialy aged.