User blog comment:Senior-Fluffy/Skips's Immortality/@comment-9769151-20140413224901

He almost died in "A Skips in Time" because, as Skips said, if Teenage Skips was in the present, then him becoming immortal never happened, time was catching up to him, and, since again he didn't become immortal with his teenage self being with him in the present, caused him to rapidly age and almost die. Hope this helps. :)