(A/N So, yeah... It gets worse before it gets better...)
Percy
He felt the years pass over him, but they no longer touched him. His primary sense of time came from his still mortal loved ones.
It baffled him how Grace changed.
Visiting his mother tended to be a solemn occasion as she aged so violently. Estelle cried for a week the first time their mother didn't recognize them. Paul held her hand and explained how it'd been getting worse but she didn't want them to worry. The doctors didn't have anything for them to do.
He sat vigil with his friends from the Argo II as Frank and Hazel came to terms with the fact they would never conceive. Hazel was technically dead. Her body wasn't born of the mortal realm, but rather a manifestation of her very soul. A soul could not reproduce. They handled it well, but a lot of their plans had to be reformed.
Piper aged gracefully. She was a wandering warrior, willing to fight for anything just. She saw love so plainly, and tried to foster it however she could. She spent more time in the Wild than among the others.
Leo died. Ares had an argument with Hephaestus and Phobos and Deimos decided they would seek vengeance on behalf of their father. Calypso sent them to reform, but the damage was done. She still didn't know how to handle being mortal and aging, and was not prepared to deal with the death of a loved one. Percy held her as she cried on his shoulder and they shared stories about Leo and his shenanigans. A week later Calypso found out she was pregnant. Percy let Hazel and Annabeth comfort her then, as he was too far out of his element.
Months later a little boy entered the world and Percy wondered about how so many of his mortal friends were growing into their families. Two had children and one couple had tried.
It wasn't too long before Sally Jackson followed Leo Valdez. Percy considered more than once asking Hades if he could visit them. Were they with Jason?
Once a month he took Paul out for lunch. Estelle joined them sometimes, but she was largely still avoiding him. Paul greyed further. Annabeth visited him too, making sure he was doing well even though he was alone. It wasn't until Percy saw Grace and Paul together that he realized the child was already 8 years old.