We know of like one day of Wanda and Pietro lives as kids and barely any for Pietro Life as a adult, for all we know Pietro could have his powers also barely just like Wanda did.
This is not a plothole. This is a retcon, and not even a particularly egregious one. WandaVision doesn't contradict Wanda's origins from Age of Ultron; it just gives us details to more fully understand her story in hindsight.
both Wanda and Pietro surviving an Infinity Stone seems to imply that both of them had powers before encountering the Stone; or possibly had something in their DNA.
I think it's stupid that the mind stone gave them the powers they have. Wanda can bend reality and Pietro can run fast, they should have been linked to the reality and space stone respectively.
