The art was great, and I loved the use of the 2D lighting system. The distribution of particles per body of lava was a tad bit off (small pockets have a lot of particles; bigger ones have them more spread out) but at that point I'm already nitpicking.
The platforming felt pretty good (but only in the younger years, although I'm guessing that's the point), although I definitely would suggest adding a friction-less physics material to the player so they don't get stuck on walls.
The final "boss" was challenging, but mostly due to the way the camera worked. The camera didn't start scrolling quickly enough, making the jump upwards tighter than it probably should've been, especially with the player getting stuck on walls occasionally. At least there was a checkpoint at the top, so restarting never felt too punishing or frustrating.
I liked the concept for the rewind mechanic, but right now there's no reason to be the old man besides an arbitrary hole in the level design (even for dodging enemies, the old man moves too slow to merit switching). Would've made for a more interesting/clever dynamic if the old man had his own skillset over the younger variant, to make up for his pathetic walking speed and jump hop (no offense, old people).
I loved the audio though. Good vibes.
Overall, I'd say you did a great job! Definitely one of the better games I've played this jam!