I think something like that was the case with me. I lost two grandfathers and a grandmother in me teens. That together with an emotional distance with my father left me very prepared for his death. More prepared than I would have thought.I still struggle with it. I'm fortunate in that I didn't lose many people close to me until I was older, but that left me more aware of their absence. I've wondered if losing a love one early is easier, because you have longer to process it, or because in your most formative years you build walls to contain the grief.
But it's hard to tell, I'm only 35, emotional wounds might flare up from nowhere at some point. Humanity is a tricky thing!