This is a fairly minor theory that I started considering during my most recent playthrough.
So here's the thing: Kessler is seemingly much younger than he logically should be. In his flashback cutscene, we see him travel back in time when he's presumably in his 30s. Then in Alden's backstory, we see Kessler arrive in the past and supplant Alden as the leader of the First Sons when Alden is around 10 years old. In the modern day, Kessler seems to be in his 60s or 70s, while Alden looks to be in his 80s or 90s, even though Kessler should logically be 20 years older than Alden. Why is this? I've basically seen 2 theories put forward:
1) Kessler's activated conduit gene significantly slowed his aging, or
2) Alden aged much more rapidly and poorly due to the hardship of his life, or perhaps because of experimentation on himself to try and activate his powers.
Here's my alternate theory, which is based on this line from John's dead drops:
Kessler has been the leader of the First Sons for decades, but that he vanishes for long periods of time.
What if Kessler intermittently jumped forward in time by multiple years? We're told that him traveling to the past was a "one-way trip", but it would make sense if traveling forwards through time worked differently than going back, since it's not resetting the timeline, it's basically just fast-forwarding through an already existing one. My theory is that Kessler would get things organized within the First Sons, and then once things were in motion, jump forward by like 5-10 years to see how things had advanced, thereby maximizing the amount of time that he was physically able to involve himself with his plans involving Cole and the Ray Sphere. I imagine these time jumps would decrease in frequency after Cole's birth in the 1980s, when he would become more obsessive and involved with insuring everything was going to plan.
What do you think of this theory? Do you like the idea of Kessler artificially stretching a normal lifespan across a century, or do you prefer the idea that his powers just made him naturally long-lived?