[ZariusTwo]

All we know about Jason post-Zeo was he spent some free time with his aunts and then went diving with a visiting Kimberly in the movie. Next thing we know he's a chubby drifter with an attitude in "Forever Red" and he has his original powers back.

There have been several "word of god" off-screen explanations for all of this, but nothing substantial on-screen.

Also, according to original series developer/writer Tony Oliver, Spike is not Kimberly's son...whilst another member of the creative team said Kimberly married Skull a while ago, so take what you want from that.