Superman's age has never been addressed. but being more powerful, I haven't seen that though....sort of like in the book of Genesis in the Bible when people lived to be 969 yeasr old etc. He'll always be a thousands steps ahead of humans. I just think he ages extremely slow, like 1 month a year, but he still ages. Why? As mentioned before, he was in a justice league episode with grey hair and comics too, still he was strong. He must also have a life expectancy because didn't superman help found the legion of superheros. In fact, they exist many years after his death. Therefore, a 188 years to 1000 years would probably be close to his maximum.