Ok, a little wild theorycrafting ahead, but it JUST appeared to me when Bopen killed Roamin with the telekinetic sword move.
Bopen is confirmed, I believe, to be a god or the child of one.
The Dragons turn into metal (Silver for the one we KNOW died).
Golstandt is the currently surviving Dragon Aspect / God. Emphasis on Gol(d).
Deadbones’ ice-cream lady from The Birth of Magic campaign was impregnated by Golstandt (via magic, but whatever), and - here’s the important bit - the baby died.
What happened when the second dragon died? It turned into a mountain’s worth of silver, and an Ageless dragon.
So my theory is as such:
Golstandt knocks up Deadbones. The baby dies, and becomes a chunk of gold. Deadbones is made Ageless by the merfolk. Sometime later - a long time later - Bopen is born or removed through some means. Maybe Ageless-DB got torn in half, or had her skull crushed. But Gold-Chunk-Bopen got out.
Then someone made a Sword out of him. And it got into the hands of that little shit princeling back in The Fall of Dundenburough(?). Then it started possessing him like a horcrux, before ‘being born’ as Bopen for the first (or second? First successful?) time, taking the prince’s bones for his first lich-puppet body.
Additional points for; Ageless… more or less stay the same once they’ve been Turned. If Bopen was turned before he was ever even born to begin with, being a creepy horror movie baby in mentality makes total sense. And Rawb himself said that Bopen was like a child, attention seeking and short of attention span.
Point against; Other elves, including however many were ‘made’ by Golstandt and the other dragon, don’t randomly turn into Gold/Silver when they die. Possibly hand-waived away by the fact that it happened during TBoM.