Steve Rogers aged due to various factors including the passage of time and the effects of his superhero adventures on his body.
Steve Rogers' aging in comics was a result of both natural aging and the cumulative stress and injuries from his battles. Also, some storylines introduced special circumstances or magic that affected his aging process.
Steve Rogers got old in comics because of a combination of normal aging and the toll that saving the world took on his physical and mental state. Sometimes, comic writers used creative plot devices to explain his aging in different ways depending on the story arc.