@Superman Consider this. There are several different lore types on demons when you research them. Most demons are considered eternal unless you manage to kill one, which means he could be anywhere from 50 to 6,000 years old at the least. Cedran is the son of a God, but he doesn't know this. Now, considering the Purge happened 100 years prior, and that the Gods are just now seeking their children to exact their revenge, you can swing this one of few ways and have it make sense.
1.) He's only 23 and has no knowledge at all about who his real father is.
2.) He's really old, but decided to come to the surface to exact his father's revenge. Unfortunately, the trip cost him his memory and he's just been wandering around doing his thing.
3.) He's really somewhere between 50 and 300 years old, but because he was born on the surface to a demoness who was likely killed somehow before he found out the truth, he doesn't know he's really the son of a God.
Those are just a few examples mind you, so you can really spin it either way you want to go.